With this caterpillar, since naturalists know what to call it, and there is no chance of its handing down any of their names in Latin to posterity, it has been possible to make experiments, and on the whole perhaps they have been in favour of the protective resemblance theory. The most interesting one—that I have read, that is to say—was made by Professor Poulton with a full-sized green lizard, and is thus described by him: “The lizard was evidently suspicious, and yet afraid to attack the caterpillar, which maintained the terrifying attitude in the most complete manner throughout. The lizard kept boldly advancing, and then retreating in fright; but at each advance it approached rather nearer to the caterpillar. After this had taken place many times and nothing had happened, the lizard grew bolder and ventured to gently bite what appeared to be the head of the caterpillar; it then swiftly retired, but finding that there was no retaliation it again advanced and gave it a rather harder bite. After a few bites had been given in this cautious manner, the lizard appeared satisfied that the whole thing was a fraud, and devoured the caterpillar in the ordinary manner.”[98] Professor Poulton has no doubt as to the lizard having been alarmed at first by the appearance of the caterpillar, and adds that he has never seen one act in the same way on any other occasion; other large hawk-moth caterpillars being eaten at once with entire _sang-froid_. It may be observed, however, that if every lizard were to act in the way recorded, under natural conditions, the advantage to the caterpillar would be nil, since though a species may survive through not being eaten, it certainly will not through being eaten with hesitation. And why should a lizard be more timid in the open air than in a box or a fern-case? Unless we assume, therefore, that this particular one was bolder than most others would be, the result of the experiment was not for, but against, the theory it was designed to test; and since we have no business to assume, the only thing to do is to get more caterpillars, and give them to more lizards. Small birds, however—and this in a country like England is more to the point—seem really to fear these pseudo-snakes to the extent of flying away from them.[99] But would an ordinary large caterpillar of the _Sphingidæ_—say, of a privet hawk or death’s-head moth—frighten them in the same way? If so, then again we are nowhere.