A hydra is a multi-headed water serpent, usually has eight heads, that breathes acid অথবা আগুন অথবা something like that, and if আপনি cut off one of it's heads, two আরো 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 দ্বারা cutting its head off and burning the tip অথবা 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