A silly sounding puzzle, with a simple solution:
A man is sleeping in his bedroom when he realizes that there is a mosquito hovering. He understands that the odds are close to certainty that the mosquito will probe his skin as he sleeps.
Without adding any barrier, chemicals, devices or effecting the mosquito in any way. What can he do to decrease his odds of a mosquito bite by a factor of 13 (Precisely)?

Invite 13 people into his room
  (assuming that he was the only person in the room)