"A few snakes do inject their venom, the rattlesnake being a well-known example. A rattlesnake's fangs are like hypodermic needles, shooting venom into prey at high pressure from a poison gland in the snake's head. But many venomous snakes and other reptiles do not have tubes in their fangs, and so cannot deliver pressurized venom. Often their fangs just have a single groove, running top to bottom."
Snake venom gets into the groove - physicsworld.com
