The plaintiffs were defeated by a defense of assumption of risk which they were content to assume was *240unaffected by 1969 legislation introducing a scheme of comparative negligence in the Commonwealth. The question whether comparative negligence should be held to displace assumption of risk was not raised by the plaintiffs, and we leave it untouched.3 We deal, then, with conventional assumption of risk.4

The plaintiffs, husband and wife, sued Moyen Construction Corp. (contractor) and Mayflower Cooperative Bank Corp. (bank) in Superior Court, Plymouth County, for injuries to the wife and consequential damage to the husband caused, so it was alleged, by negligence of the defendants. Trespass and nuisance were also alleged.5 At the close of the plaintiffs’ case, the judge directed a verdict for the bank. The action continued against the contractor and, when all the evidence was in, a special verdict was taken with the jury finding in answer to the first question that the plaintiff wife assumed the risk of injury (this rendered answers to other questions unnecessary).6 Accordingly judgment entered for both defendants.7 The plaintiffs’ appeal on *241points of law raised below reaches this court by transfer on our own motion. We affirm.

These were the facts. The plaintiffs resided at No. 97 Court Street, Plymouth, and jointly owned the house opposite, No. 96j which they operated as a rooming house. As one crossed the street from No. 97 to No. 96, one saw No. 94, a private house, to the left, with an alley between some fifteen to twenty feet wide, and No. 98, also a private house, to the right, with an alley between about six to eight feet. In June, 1973, No. 94 was owned by the bank and being converted by the contractor into a bank unit by means of structural changes which included dismantling a chimney and removing interior plaster and lathing.

On the afternoon of June 17, a Sunday, Mrs. Haley wanted to get into the cellar with an outside entrance at the center rear of No. 96, in order to locate a bed she would need the next day. She crossed the street and, looking to the left of No. 96, discovered that there was a dense, tangled mass of debris spread through that alley, obviously the temporary outflow of the construction work at No. 94. Mrs. Haley had the alternatives of making her way down that alley, or going through No. 96 to the rear, or walking down the alley to the right. The first route, the one she took ordinarily, now involved a chance of accident; the second, a possible embarrassment, as she would have to pass through a room which might have been let to a roomer (she did not say whether it had been); the third, some discomfiture, because she might set off barking by a Labrador, secure behind the fence of No. 98 (Ulber Tarantino, owner of that house, would not object to Mrs. Haley’s using the cement path running the length of the alley on his side of the property line). Mrs. Haley chose the first course and picked her way in gingerly fashion to the cellar. After finding the bed, Mrs. Haley, emerging from the cellar, again faced a similar choice. She elected to return through the debris, and this time she stumbled and fell, suffering back and neck injury. It needs to be added that some of the testimony put the property line between Nos. 94 and 96 at eleven inches from No¡ 96, other *242testimony at five to six feet. In all probability, Mrs. Haley passed from one to the other side of the line (wherever exactly it was located) as she made each trip. She fell toward No. 94, but whether the length of her body on falling was wholly to one side or the other of the line, or across it, must remain in doubt.8 To round out the facts, the evidence allowed an inference that rubbish had accumulated in the alley before the weekend of June 16, and that the bank sent representatives to check on the progress of the construction and had opportunity to observe the condition.

1. Liability of the defendant contractor, (a) The first question put to the jury, and answered by them affirmatively, was: “Did the plaintiff, Barbara Haley, knowingly assume the risk of injury?” The judge’s instructions tried hard to put the concept to the jury in intelligible form consistent with the decided cases. There was objection that a supplemental charge in response to a request from the jury did not sufficiently stress the requirement that Mrs. Haley must comprehend fully the risks involved and assume them voluntarily. See Uloth v. City Tank Corp., 376 Mass. 874, 882 (1978); Crone v. Jordan Marsh Co., 269 Mass. 289, 291 .(1929); Fitzgerald v. Connecticut River Paper Co., 155 Mass. 155, 158 (1891). Again the plaintiffs complained that that charge did not adequately stress the “subjective” element in assumption of risk. See Uloth, supra; Kitchen v. Women’s City Club, 267 Mass. 229, 231 (1929). But we think these criticisms are not well founded; as to the last, the plaintiffs miss the point that state of mind may be inferred from external signs. See McCarthy v. Morse, 197 Mass. 332, 335-336 (1908); W. Prosser, Torts § 68, at 448 (4th ed. 1971); Bestatement (Second) of Torts § 496D, Comment d (1965).9

*243(b) There is no suggestion that the evidence was insufficient to warrant the jury in their answer “Yes” to the question, and, as indicated above, the plaintiffs are not in a position to urge that assumption of risk was not a permissible defense to the case so far as it was premised on negligence. But the plaintiffs seek to argue that the defense was not available to so much of the case as was predicated on “trespass” (or “nuisance,” not differentiated significantly here from trespass).10 By instructing the jury that they need not go beyond the first question if their answer to it was affirmative, the judge was holding implicitly that the defendant could defend on assumption of risk even if the facts were taken in their best light for the plaintiffs, i.e., that Mrs. Haley tripped over debris on her side of the line where she was thoroughly privileged to be. The judge’s implicit ruling was correct, for the authorities have not distinguished, for purposes of the availability of the defense, between defendant’s negligence and defendant’s relatively innocent, or nondesigning, or nonpurposeful trespass. See Sherman v. Fall River Iron Works Co., 2 Allen 524, 526 (1861); Fresno Air Serv. v. Wood, 232 Cal. App. 2d 801, 807 (1965); Con-nolley v. Omaha Pub. Power Dist., 185 Neb. 501, 508 (1970); Kopka v. Bell Tel. Co., 371 Pa. 444, 453 (1952). See also 2 F. Harper & F. James, Torts § 22.8, at 1222 (1956). Cf. Victor v. Sell, 301 Minn. 309, 314-315 (1974) (“intentional” trespass). The facts would not warrant a trier in attaching a harsher characterization to the trespass here.

We have dealt thus seriously with the argument about “trespass” even though there is considerable doubt whether it was advanced below, or advanced with sufficient clarity.* 11 *244Moreover there is a certain unreality in seeking to make lia bility turn here on niceties of location.12 The plaintiffs indeed almost admit as much when they say the “primary thrust” of their case was negligence.

2. Liability of the defendant bank. In directing a verdict for this defendant, the judge evidently believed that it had shed responsibility for the spillage of debris by contracting for the construction with an “independent contractor.” However, there is doubt whether the contracting-out can absolve the owner of responsibility for an unreasonably dangerous condition created by the contractor, where the owner has knowledge of the condition. See Rockport v. Rockport Granite Co., 177 Mass. 246, 255 (1901); Kraus v. Alamo Natl Bank, 586 S.W.2d 202, 206 (Tex. Civ. App. 1979); Ventoza v. Anderson, 14 Wash. App. 882, 896 (1976); Restatement (Second) of Torts § 414A (1965). But if there was error in directing the verdict for the bank on the ground assigned — a matter we do not decide — the error was inconsequential, since the finding against the plaintiffs and for the defendant contractor with respect to assumption of risk should extend by way of collateral estoppel to defeat the plaintiffs’ claim regarding the bank. See Carpenter v. Suffolk Franklin Sav. Bank, 370 Mass. 314, 322 (1976); Maher v. General Motors Corp., 370 Mass. 231, 234 (1976); Restatement (Second) of Judgments § 88 (Tent. Draft No. 3, 1976).

*245There is nothing in the idea that a jury might be unjustly predisposed in favor of the contractor because they observed the bank being let off (we assume, improperly) early in the case. This is speculative at best, and seems intrinsically unlikely, as the responsibility of the contractor on the scene would appear more direct than the bank’s.

Judgments affirmed.