A photon checks into a hotel, takes his room keycard, and makes to go to the lift. The man at the desk calls after him, "do you have any luggage you'll need a hand with?"
"No," says the photon. "I'm travelling light."
Blame Sarah... *g*
Along the same lines:
Two hydrogen atoms. One says to the other, "I just lost an electron!" "Are you sure?" his friend asks. "Yes, I'm positive."
