One night three of the vampires

One night, three of the vampires turn into bats and fly off.

An hour later, the first vampire comes back with blood dripping from his fangs.

“See that mansion over there?” he asks. The other vampires nod. “I sucked the blood of five people in there.”

An hour later, the second vampire comes back with blood completely surrounding his mouth.

“See that mansion over there?” The other vampires nod. “I sucked the blood of ten people in there.”

An hour later, the third vampire comes back thoroughly covered in blood. “See that mansion over there?”

The other vampires nod.

“I didn’t.”