“(17.2. 1914) Beyond some bars, out of arm's reach, lies an objective [a banana]; on this side, in the background of the experiment room, is placed a sawn-off castor-oil bush, whose branches can be easily broken off. It is impossible to squeeze the tree through the railings, on account of its awkward shape; besides, only one of the bigger apes could drag it as far as the bars. Sultan is let in, does not immediately see the objective, and, looking about him indifferently, sucks one of the branches of the tree. But, his attention having been drawn to the objective, he approaches the bars, glances outside, the next moment turns round, goes straight to the tree, seizes a thin slender branch, breaks it off with a sharp jerk, runs back to the bars, and attains the objective. From the turning round upon the tree up to the grasping of the fruit with the broken-off branch, is one single quick chain of action, without the least 'hiatus', and without the slightest movement that does not, objectively considered, fit into the solution described.”

Source: The Mentality of Apes, 1925, p. 94; As cited in: Arthur Koestler, The Act of Creation, 1964, p. 103