Vampire tongue
Humans have been subject to one of the most successful disinformation campaigns ever waged, to wit: vampires. Vampires do exist; they mimic human form almost perfectly. They can eat human food, though they vastly prefer meat dishes. They don’t turn into bats. They do tend to be more intelligent and physically quicker and stronger than humans. Their senses of hearing, sight, smell, taste, and touch are significantly more sensitive than human.
The one physical feature that sets them apart is their tongues.
The underside of a vampires tongue has a small circular rasping mouth, like a lamprey. Their saliva contains powerful anti-coagulents, and more importantly, a highly addictive drug that gives a subtle high while blocking the pain of the teeth rasping a small hole in the skin. They don’t drink much blood at a time, but, like some insects, they need a blood meal to reproduce.