They are very mobile in their own way. Most of them live in the tropics. Few snake species live beyond the Tropic of Cancer or Tropic of Capricorn, and only one species, the common viper ("Vipera berus") lives beyond the Arctic Circle. They can see well enough, and they can taste scents with their tongues by flicking them in and out. They are very sensitive to vibrations in the ground. Some snakes can sense warm-blooded animals by thermal infrared.