Bat Mass: Fantasy

Everybody expects bar stools to be built #sturdy, to support regular patrons and quickly end irregular fights. In Pat's bar, you might notice the extra-wide windowsills and wonder why. It's because of the vampire bats' conservation of mass.

Inspiration: sturdy
Potential: Low. As a setting, this is just funny to me.
Notes: Magic makes them fly, but it doesn't make them light. Urban fantasy or possibly humorous regular low fantasy.