Is my cat a vampire?

Can you explain this odd behavior that my cat is exhibiting?

Only at night does he do this. He’ll get this creepy look in him and all of the sudden go up to my other cat and bite onto the back of his neck. My other cat seems to be subdued for a bit, but then doesn’t like it and will cry and try to get him off. He is not biting hard enough to draw blood or anything, so I know he’s not trying to physically harm him. He will then continue to do it a few more times. It’s not every night this happens, but often enough that it is freaking me out. This behavior has been going on for about 2 months now.

So, is my cat a vampire? Have you seen this before? What can I do to stop it?