You have a couple of options depending on budget:

1.For the best continuity and fastest application (and probably the most expensive):
Christian Tinsley transfers with blood gel, dried blood or blood on top.

2.For cheapo prosthetics (and I mean cheap) and good continutity:
Woochie + rubber mask grease (to color prosthetic) + various blood products.

3.For cheapest and hardest continuity:
thin layers of Scar material or gelatin, punch hole in with end of a pen cap, make the edges jagged, fill with various blood product.

Depending on how old the bite is, don't forget to bruise around the bites- a little fresh redness on new bites, deeper red +lighter purple for 1-2 days old, dark purple/green/yellow for older. The bruising will make the area around the bite look more raised too.

Good luck!!