How did Thorndike's puzzle box work?

Edward L. Thorndike, answered from the texts and cited to the page.

Edward L. Thorndike answers

Put a hungry cat in a wooden box — fifteen by ten by sixteen inches, with bars for walls — and watch what happens.¹ The animal shows every sign of distress at its confinement: it squeezes at the gaps between the bars, claws and bites at the wire, thrusts its paws through any opening it can find, and struggles with a vigor that is, frankly, extraordinary — eight or ten minutes of incessant effort without pause.²

Outside the box sits the food. The cat does not reason toward it. It does not study the mechanism and deduce the solution. It simply strains against everything. The box is built so that one particular act — pulling a wire loop, turning a wooden button from vertical to horizontal, pressing a lever — releases the bolt and lets the door fall open.³

Care was taken to place that mechanism away from the widest gaps in the bars, because a cat attacks the large openings first by instinct, and if the release happens to sit near one of them, instinct does the work and you learn nothing about association.⁴ The mechanism must be met by accident, not by the animal's natural first assault. And that is precisely what occurs.

Among all the clawings and squeezings, some one movement happens to catch the loop or turn the button, the door opens, and the cat gets out to its food.⁵ Put it back. The useless movements come a little less; the successful one comes a little sooner. Trial by trial the curve descends — not by a sudden leap of understanding, but by the gradual stamping-in of the one connection that paid, and the stamping-out of everything that did not.⁶

What began as promiscuous struggle narrows, over many repetitions, to a single definite act performed without delay the moment the animal is placed in the box. That is the law of effect made visible. A situation arouses, by instinct or by accident, a welter of impulses and acts; the one that secures freedom is stamped in by the pleasure that follows it; the rest are stamped out.⁷

No ideas, no reasoning, no insight into the relation between button and door — only the selection of a response by its consequences. The chick in the pen and the kitten at the button are doing the same thing, and so, I would argue, is the child learning arithmetic.

Sources

The size of this box was I5 x 10x 16.
Animal Intelligence
When put into the box the cat would show evident signs of discomfort and of an impulse to escape from confinement. It tries to squeeze through any opening; it claws and bites at the bars or wire; it thrusts its paws out through any opening and claws at everything it reaches... For eight or ten minutes it will claw and bite and squeeze incessantly.
Animal Intelligence
make in this front side a door arranged so as to fall open when a wooden button inside is turned from a vertical to a horizontal position
The Human Nature Club
Especial care was taken not to have the widest openings between the bars at all near the lever, or wire-loop, or what not, which governed the bolt on the door. For the animal instinctively attacks the large openings first, and if the mechanism which governs the opening of the door is situated near one of them the animal's task is rendered easier.
Animal Intelligence
Some one of all these promiscuous clawings, squeezings, and bitings turns round the wooden button, and the kitten gains freedom and food.
The Human Nature Club
gradually all the other non-successful impulses will be stamped out and the particular impulse leading to the successful act will be stamped in by the resulting pleasure, until, after many trials, the cat will, when put in the box, immediately claw the button or loop in a definite way.
Animal Intelligence
A certain situation arouses, by virtue of accident, or, more often, instinctive equipment certain impulses and corresponding acts. One of these happens to be an act appropriate to secure freedom. It is stamped in in connection with that situation.
The Elements of Psychology