Tongue-flicking is a sensory-gathering behavior used by snakes to deliver odorants to the vomeronasal organ. In the present study we provide a detailed description of environmental control and motor patterns of tongue-flicking in garter snakes, Thamnophis sirtalis. Tongue-flicks were monitored during prey extract trailing, foraging, delivery of air-borne odors and in an open field. Tongue-flick rates increased during airborne odor delivery and as a function of prey extract concentration during trailing, as previously reported. Motivation and prey consumption appeared to modify tongue-flick patterns since 1. tongue-flick rates were higher under foraging conditions than in an open field where no prior prey consumption had occurred and no prey odors were present; and 2. tongue-flick rates were elevated after prey consumption. The number of oscillations and the duration of tongue extensions were significantly reduced following tongue-substrate touches, suggesting that tongue contact with the substrate is the immediate stimulus for tongue retraction.