One of the oddest and hardest to explain conditions of a vampire is that they have no reflection. Maybe a spell made so humans could easily identify vampires. Or side effect of having their bodies preserved and held together by magic. Clothing the vampire is wearing also doesn't show up, I assume this must be because whatever a vampire is wearing or holding is theirs and part of them (The same reason a vampire's clothes will disappear when they are dusted.) The clothing is surrounded by the vampire's aura, and basically part of them.