Some one may object that, true as all this may be, the intelligent acts reported of animals are in many cases such as could not have happened in this way by accident. These anecdotes of apparent comprehension and inference are really the only argument which the believers in reason have presented. Its whole substance vanishes if, as a matter of fact, animals can do these supposed intelligent acts in the course of instinctive struggling. They certainly can and do. I purposely chose, for experiments, two of the most intelligent performances described by Romanes in his Animal Intelligence--namely, the act of opening a door by depressing the thumb-piece of an ordinary thumb-latch and the opening of a window by turning a swivel (see pp. 420-422 and p. 425 of Animal Intelligence, by G. J. Romanes). Here I may quote from the detailed report of my experiments (Monograph Supplement to the Psychological Review, No. 8): "G was a box 29 × 20-1/2 × 22-1/2, with a door 29 × 12 hinged on the left side of the box (looking from within), and kept closed by an ordinary thumb-latch placed fifteen inches from the floor. The remainder of the front of the box was closed in by wooden bars. The door was a wooden frame covered with screening. It was _not_ arranged so as to open as soon as the latch was lifted, but required a force of four hundred grammes, even when applied to the best advantage. The bar of the thumb-latch, moreover, would fall back into place again unless the door were pushed out at least a little. Eight cats (Nos. 1, 2, 3, 4, 5, 6, 7, and 13) were, one at a time, left in this thumb-latch box. All exhibited the customary instinctive clawings and squeezings and bitings. Out of the eight, _all succeeded, in the course of their vigorous struggles, in pressing down the thumb-piece_, so that if the door had been free to swing open they could have escaped. Six succeeded in pushing both thumb-piece down and door out, so that the bar did not fall back into its place. Of these, _five succeeded in also later pushing the door open, so that they escaped and got the fish outside_. Of these, three, after about fifty trials, associated the complicated movements required with the sight of the interior of the box so firmly that they attacked the thumb-latch the moment they were put in." In the cases of No. 1 and No. 6 the combination of accidents required was enough to make their successes somewhat rare. Consequently weariness and failure offset the occasional pleasure of getting food, and after succeeding four and ten times respectively they never again succeeded, though given numerous opportunities. Their cases are almost a perfect proof of the claim that accident, not inference, makes animals open doors. For they hit upon the thing several times, but did not know enough to profit even by these experiences, and so failed to open the door the fifth and eleventh times.