A hydra is a multi-headed water serpent, usually has eight heads, that breathes acid au moto au something like that, and if wewe cut off one of it's heads, two zaidi grow back.
a Lernaean Hydra is a Greek sea serpent legend that usually has 9 heads, cut one off and two grow back on. the only way to kill a hydras head is kwa cutting its head off and burning the tip au freeze it solid like in Percy Jackson and the lightning thief (can't remember how has something to do with the lady with snake hair).:D