In medieval literature, the ichneumon or echinemon was the enemy of the dragon. When it sees a dragon, the ichneumon covers itself with mud, and closing its nostrils with its tail, attacks and kills the dragon. The ichneumon was also considered by some to be the enemy of the crocodile and the asp, and attack them in the same way. The name was used for the "pharaoh's rat", mongoose, or Egyptian mongoose, which attacks snakes; it can also mean "otter".
Etymology
Ichneumon (ἰχνεύμων) means "tracker" in Greek. Cockatrice, a name for another mythical beast, derives from calcatrix, a Latin translation of this. The Ichneumon was one of the few who can look at a cockatrice without turning to stone.
References
Ichneumon (medieval zoology) Wikipedia(Text) CC BY-SA