Release of the envenomated prey reduces the risk the snake faces from retaliation the rodent might inflict with a bite of its incisor teeth. But, released prey may scamper beyond the immediate vicinity of the snake and must be relocated. Relocation presents another set of problems to the snake. Envenomated fishes or frogs in a water current might be carried away, or birds on land might fly beyond a recovery range, and these prey are sometimes held by the snake (Hayes and Duvall, 1991). Some tree vipers, which would lose released prey to the forest floor below, also commonly hold struck prey. Even released rodents may travel some distance and disappear from visual or thermal view, leaving only a chemical trail of cues to follow. But these scent trails of the envenomated prey cross the scent trails of other rodents within the local colony frustrating the ability of the snake to track the envenomated prey. However, rattlesnakes can distinguish the scent of an envenomated mouse from that of even a litter-mate, leading to the suggestion that the suite of chemicals in venom includes some principles that increase the perceptibility of the prey during poststrike trailing (Chiszar et al., 1983; Furry et al., 1991). There is support for this view. If given the choice of poststrike trails between that of an envenomated prey and of a nonenvenomated litter-mate, rattlesnakes preferentially follow the scent trail produced by the envenomated mouse (Chiszar et al., 1990; Robinson and Kardong, 1991). However the chemosensory capabilities of rattlesnakes are more acute than this. If the venom ducts of a rattlesnake are surgically ligated, the snakes still orient to and strike prey accurately, but because of the duct ligations, no venom is delivered. These "venectomized" snakes then begin normal poststrike trailing behavior. Even in the absence of injected venom, these snakes are still able to distinguish the scent trail of the mouse they struck (but no venom) from the scent trail of this same mouse laid before being struck (Lavín-Murcio et al., 1993). Apparently, fang penetration alone produces a distinctive change in the perceptibility of the struck mouse which permits the snake to distinguish its poststrike from its prestrike odor. Therefore, the chemosensory ability of rattlesnakes is very acute, discriminating between subtle differences in mouse scent.

See:  Lavín-Murcio, P., B.G. Robinson, and K.V. Kardong. 1993. Cues involved in relocation of struck prey by rattlesnakes, Crotalus viridis oreganus. Herpetologica. 49(4):463-469.