a rattlesnake
Examples
When you see a rattlesnake poised to strike you, do not wait until he has struck before you crush him.
After a hard day of basic training, you could eat a rattlesnake.
I loved her like a rabbit loves a rattlesnake.
A rattlesnake that doesn't bite teaches you nothing.
He will fight a rattlesnake and give it the first two bites too.
A rattlesnake loose in the living room tends to end all discussion of animal rights.