In these cases, as in that of ferocious animals, it is no excuse that the defendant did not know, and could not have found out, the weak point from which the dangerous object escaped. The period of choice was further back, and, although he was not to blame, he was bound at his peril to know that the object was a continual threat to his neighbors, and that is enough to throw the risk of the business on him. I now pass to cases one degree more complex than those so far considered. In these there must be another concomitant circumstance known to the party in addition to those of which the knowledge is necessarily or practically proved by his conduct. The cases which naturally suggest themselves again concern animals. Experience as interpreted by the English law has shown that dogs, rams, and bulls are in general of a tame and mild nature, and that, if any one of them does by chance exhibit a tendency to bite, butt, or gore, it is an exceptional phenomenon. Hence it is not the law that a man keeps dogs, rams, bulls, and other like tame animals at his peril as to the personal damages which they may inflict, unless he knows or has notice that the particular animal kept by him has the abnormal tendency which they do sometimes show. The law has, however, been brought a little nearer to actual experience by statute in many jurisdictions. Now let us go one step farther still. A man keeps an unbroken and unruly horse, knowing it to be so. That is not enough to throw the risk of its behavior on him. The [158] tendency of the known wildness is not dangerous generally, but only under particular circumstances. Add to keeping, the attempt to break the horse; still no danger to the public is disclosed. But if the place where the owner tries to break it is a crowded thoroughfare, the owner knows an additional circumstance which, according to common experience, makes this conduct dangerous, and therefore must take the risk of what harm may be done. /1/ On the other hand, if a man who was a good rider bought a horse with no appearance of vice and mounted it to ride home, there would be no such apparent danger as to make him answerable if the horse became unruly and did damage. /2/ Experience has measured the probabilities and draws the line between the two cases. Whatever may be the true explanation of the rule applied to keeping tigers, or the principle of Rylands v. Fletcher, in the last cases we have entered the sphere of negligence, and, if we take a case lying somewhere between the two just stated, and add somewhat to the complexity of the circumstances, we shall find that both conduct and standard would probably be left without much discrimination to the jury, on the broad issue whether the defendant had acted as a prudent man would have done under the circumstances.