Allen, J.
The immediate question of fact to be determined was why the car flew back. The plaintiffs contended that the reason was because the hooks were bent, defective, and rusty, so that they would not catch upon the truck frame. The defendant denied that the hooks were in that condition, and offered evidence tending to show that the hooks and the car were in good order *127both before and after the accident, and was allowed to introduce other evidence tending to show that the flying back of the car could be otherwise accounted for. The first piece of evidence of this character was the testimony which tended to show that a block could be and was so used in tipping the car that the hooks would not catch. If the evidence had gone so far as to show that a man was seen using the block at the time upon the very car which caused the injury to the plaintiffs, and that it had the effect to prevent the hooks from catching at that very moment, no one would doubt that the evidence would have been clearly relevant. The evidence did not go so far as this, but it was circumstantial evidence tending to establish the same thing; that is to say, there was evidence that a block could be so used, that a man was there provided with such a block, that he knew how to use it for that purpose, and that he was in fact so using it on other cars immediately before the accident. From these facts a legitimate argument might be urged that he was there for the purpose of so using the block, and that he in fact so used it upon the car which caused the accident. If it were a criminal offence to use such a block in that way, and if that particular person were under indictment for so using it on this particular occasion, it seems clear that the evidence introduced by the defendant to show the good condition of the car and of the hooks before and after the accident, and to show the opportunity, means, and knowledge of that person, would be competent evidence tending to show his guilt. In like manner, the evidence was competent in behalf of the defendant, as tending to meet and disprove the case of the plaintiffs, by showing that the accident was probably not due to a defect in the car.
The evidence of the defendant’s expert was competent for similar reasons. It tended to show that the accident could be accounted for otherwise than by reason of a defect in the car. When he stated that a car might be in perfectly good order, and still fly back by reason of the fault of those that dumped it, it was not erroneous to allow him to add that he had seen it done. This served to show more clearly the value and weight of his opinion. Commonwealth v. Leach, 156 Mass. 99, and cases there cited.
Exceptions overruled.