In Experiment I, homogenized rodent tissue was applied to the lips of prairie rattlesnakes (Crotalus viridis). This treatment produced elevated rates of tongue flicking compared to controls that received water, but the elevations seen following stimulation with homogenate were not as large as those seen after snakes struck prey. In Experiment II, water, rodent blood, and integumentary cues were applied to the lips of rattlesnakes, and only blood resulted in elevated rates of tongue flicking. We conclude that blood is a critical component of the homogenate . It is hypothesized that detection of blood during predatory strikes may be a causal element in the triggering of strike-induced chemosensory searching, a typical component of rattlesnake predatory behavior.