It's just two Capri sun straws up there

I saw a "vampire slayer" book once that had fake anatomy drawings showing hollow straw fangs and I've been haunted by it since. Absolutely does NOT work that way; if the fangs are hollow it's for injecting venom, not as a substitute for a proboscis - but that's biologically pretty risky since they're usually operating with a bite-and-hold technique. Proper answer is just solid piercing teeth that can handle a 100+lb entity struggling to break free.

I mean, the blood comes out on its own if you're bitten

osmosis. just need to get the teeth and the blood close tbh

I think it depends on the vampire TBH. Sometimes it's pretty clearly they got suction teeth and sometimes they do it real vampire style where they bite and then just suck or lick at wound.

hollow tongue theory