I don't have a pet anymore (besides the usual: spiders, flies and a brother)
But I had some hamsters.
One was a real killing hamster! D: She was born at my house because I bought the mother pregnant and I didn't know D: There were 5 children and I kept the mother and the killer hamster XD Well, she was the weakest/last to be born (at least she looked like she was the most slim at the beginning). And I think because of that she got a strong personality and had to fight for the food.
Well, she didn't bite at the beginning. But after she got mature she started to bite. She also liked to store all the food in her hiding place XD So if you gave her food she would "vacuum every little corn". That was also the only time were you could pet her without having to fear to be bitten by her.
Keyhole drawn by Yuri Iwamoto <3
Spoiler: Secret Santa gift from Commi-Ninja <3
A Black Organization Christmas Carol (need to fix the link)
XDXDXD My friend used to have an evil gerbil. It died a few years ago, but my most vivid memory of it was picking it up and my friend advising me "If it tries to jump out of your hand, punch it in the face; if it tries to take over the world, give it a cookie!" It was all the funnier at the time because the thing was such a little Houdini and so destructive that the latter was a very real possibility XDXD