During this day (29th) I observed that the pressure of the egg and young robin against his sides irritated the cuckoo: he was continually moving, jerking and wriggling his lumpish body this way and that, as if to get away from the contact. At intervals this irritation would reach its culminating point, and a series of mechanical movements would begin, all working blindly but as surely towards the end as if some devilish intelligence animated the seemingly helpless infant parasite. Of the two objects in the nest the unhatched egg irritated him the most. The young robin was soft, it yielded when pressed, and could be made somehow to fit into the interstice; but the hard, round shell, pressing against him like a pebble, was torture to him, and at intervals became unendurable. Then would come that magical change in him, when he seemed all at once to become possessed of a preternatural power and intelligence, and then the blind struggle down in the nest would begin. And after each struggle--each round it might be called--the cuckoo would fall back again and lie in a state of collapse, as if the mysterious virtue had gone out of him. But in a very short time the pressure on his {17} side would begin again to annoy him, then to torment him, and at last he would be wrought up to a fresh effort. Thus in a space of eight minutes I saw him struggle four separate times, with a period of collapse after each, to get rid of the robin's egg; and each struggle involved a long series of movements on his part. On each of these occasions the egg was pushed or carried up to the wrong or upper side of the nest, with the result that when the bird jerked the egg from him it rolled back into the bottom of the nest. The statement is therefore erroneous that the cuckoo knows at which side to throw the egg out. Of course he _knows_ nothing, and, as a fact, he tries to throw the egg up as often as down the slope.