Hiccup

This is a riddle. It works well if you let the students ask yes and no questions about the situation, before revealing the answer.
Q: A man goes into a bar and asks for a glass of water. The barman pulls out a gun, and points it at the customer. "Thank you" replies the customer and walks out. What happened?
A: The customer had hiccups.
  (It always works - a shock as a hiccup cure appears to be an international thing.)