I was interested in the significance of the yawning behaviour, and found this
really cool research paper! I hope you can access it. I'm at an academic site...
Rattlesnakes will trail prey that they themselves have struck for up to 24 hours. They will not trail unstruck prey or prey struck by other rattlers.
For our study, the prestrike behaviors observed in the baseline studies (no strike)
appeared to be analogous to ambush behavior in the wild wherein the snake
initially locates an area with high prey density and then sets up in ambush
(Duvall et al., 1985, 1990). During prestrike, there is little advantage for a
snake to indiscriminately follow odors trails of non-envenomated mice.
In this context, the yawning behavior observed, especially during baseline
experiments, is provocative. It has been argued that this yawning behavior
serves a number of functions, wiping the fangs, priming the musclo-skeletal
system for a strike, and vomeronasal function (Graves & Duvall, 1985;
Young, 1993; Schwenk, 1995). This last function seems plausible in these
rattlesnakes. The yawning during baseline experiments correlates with the
time the rattlesnake might be expected to attempt to gather environmental
odors in a refreshed vomeronasal organ (VNO). The olfactory epithelium
can be refreshed by increased ventilation. But the blindended vomeronasal
organ might retain old odors. Once the VNO becomes saturated with odors,
making odor discrimination difficult, the snake yawns and thus causes a
pressurec hange in the mushroom-bodiedV NO. This, in a sense, would clear
the VNO, allowing for a sampling of new odors (Schwenk, 1995)