When a snake flicks its tongue, it is smelling the air. Snakes recognize their owner's by their smell, and recognize other people with whom they frequently interact. When a snake's tongue touches you, it has a light, feathery touch that may tickle a bit. Venomous snakes have these teeth, plus special teeth, called fangs, that are used to deliver the venom. Some have fangs near the front of their mouth, others have fangs towards the rear of their mouths.
Lizards have teeth, too, even vegetarian lizards like green iguanas.
Some snakes have stingers in their tails. No snakes have stingers in their tails. Some have hard skin on their tail tip that may be due to a variety of reasons, such as unshed skin or new scales emerging as the snake is growing. Some burrowing snakes may have a hardened tip on their tail that they use to push against the ground to give them some leverage as they burrow new tunnels. Some snakes are vegetarians.