FusionDex

The many ears on Nidoki's ring give it an excellent sense of hearing, making it nearly impossible to sneak up on. The teeth of its key can inject a powerful poison in those who agitate it enough to make it attack.

It never lets go of a key that it likes, so people give it the keys to vaults and safes as a way to prevent crime. The male Nidoran has developed muscles that freely move its ears in any direction.