Look at the pasties

When you are trying to hide laughter from someone.
You would 'Look at the pasties' when the laughter being seen would be damaging.

Tom and Jen played a prank on Dad by putting a joke ticket on his car, but had to hide their laughter as he approached by looking at the pasties.

Dude, she walks funny- its hilarious!! We need to look at the pasties so she doesn't see us.