Why Snape doesn't have to be human

[Esmerelda Gertrude Potter-Granger]

No: HPFGUIDX 107706

I think Snape is a bat animagus, which is how he spies on the Death 
Eaters. There are a few bat references made in relation to Snape so 
I can see why people make the vampire connection. Although since JKR 
nixed that, I think Snape can transform into a bat- also his 
character is quite bat-like.

"Esmerelda Gertrude Potter-Granger"