When exposed to an anesthetized snake, feral black-tailed prairie dogs living in a high-snake-density area approached ambivalently and investigated the snake, typically near the head. Snake-investigation was interrupted intermittently, when the prairie dog jumped away, foot thumped or jump yipped, and approached the snake again. This behavior attracted other prairie dogs, who behaved similarly. Message analyses of two apparent signaling acts — foot thumping and jump yipping — demonstrated that they convey information that withdrawal from the snake has become less likely, and continued interaction with the snake more likely. Prairie dogs in a zoo and feral prairie dogs in a low-snake-density area were unresponsive to immobile snakes, but reacted strongly when the snake was permitted to move. We compared these results to similar data on California ground squirrels and discussed the selection pressures, and ontogenetic and perceptual processes that may have acted as determinants of this snake-directed behavior.