Presently, when the whole of the vocalists had reached their highest notes, they became hushed in an instant. I was amazed at this, and began to wonder at the sudden termination of the concert. But, looking about, I observed a brown owl drop down, with the silence of death, on to the top of a low dyke close by the orchestra.[133] _Reptiles._ Like the other cold-blooded Vertebrata, the reptiles are characterised by a sluggishness and low development of mental power which is to some extent proverbial. Nevertheless, that some members of the class present vivid emotions is not to be questioned. Thus, to quote from Thompson:-- The common guana (_Lacerta iguana_) is naturally extremely gentle and harmless. Its appearance, however, is much against it, especially when agitated by fear or anger. Its eyes then seem on fire; it hisses like a serpent, swells out the pouch under its throat, lashes about its long tail, erects the scales on its back, and extending its wide jaws, holds its head, covered over with tubercles, in a menacing attitude. The male, during the spring of the year, exhibits great attachment towards the female. Throwing aside his usual gentleness of character, he defends her even with fury, attacking with undaunted courage every animal that seems inclined to injure her; and at this time, though his bite is by no means poisonous, he fastens so firmly, that it is necessary either to kill him or to beat him with great violence on the nose, in order to make him quit his hold.[134] Several species of snake incubate their eggs and show parental affection for their young when they are hatched out; but neither in these nor in any other of their emotions do the reptiles appear to rise much above the level of fish. The case, however, which I shall afterwards quote, of the tame snakes kept by Mr. and Mrs. Mann, seems to show a somewhat higher degree of emotional development than could be pointed to as occurring in any lower Vertebrata. Moreover, according to Pliny, so much affection subsists between the male and female asp, that when the one is killed the other seeks to avenge its death; and this statement is so far confirmed--or rather, its origin explained--by Sir Emerson Tennent that he says when a cobra is killed, its mate is often found on the same spot a day or two afterwards. Passing on to the general intelligence of reptiles, we shall find that this also, although low as compared with the intelligence of birds and mammals, is conspicuously higher than that of fish or batrachians.