The mechanism involves restricting blood flow out of the head so that pressure rises in the ocular sinus until the thin wall ruptures at a controlled point, sending a stream from the corner of the eye. It is not a routine response; the lizard first relies on camouflage, then on flattening, then on the horns and body inflation, and only some individuals resort to blood squirting at all.
What makes the behaviour interesting is that it is selective. Canid predators, in tests and observations, react strongly, shaking their heads and wiping their mouths, while birds such as roadrunners and snakes appear indifferent. That pattern points to a chemical in the blood that is aversive to canids specifically, plausibly related to the lizard's diet of harvester ants and their venom alkaloids, though the compound has not been conclusively identified.
The species has declined across much of Texas and Oklahoma, associated with the spread of imported red fire ants displacing harvester ants, pesticide use and habitat conversion, and it holds protected status in several states.