So I squeezed her knee and she stayed heroically, deliberately stoic. Then I squeezed harder and she made a little gurgling noise like she was about to ralph. She looked like she was going to ralph too. But, determined not to be silly, she didn't laugh or even giggle, not even smile [which, for her, is a part of breathing]! By this point normally she'd be convulsing on the floor hysterically.
So I decided to pull out all the stops and I really gave her something to laugh about... I squeezed just in the right spot with just the right pressure. With completely overlydeliberate calmness she said: