Mark Frauenfelder of Boingboing posted a Physics MC quiz:
This is a stumper. If a can of compressed air is punctured and the escaping air blows to the right, the can will move to the left in a rocket-like fashion. Now consider a vacuum can that is punctured. The air blows to the left as it enters the can. After the vacuum is filled the can will
a) be moving to the left
b) be moving to the right
c) not be moving
As always, the answers (including explanation) submitted are interesting read and review a lot about mis/concept of Physics. All the submitted answers are here.