Chasing Amy - Joey Laurn Adams Smile.
In the scene close to the end where Holden has Banky and Alyssa sat down and is talking to them about having a threesome. In one of the shots Alyssa is supposed to look upset. If you look just right when she has her hand over her eyes looking down, you can see she is smiling! You can tell she is almost about to laugh a little too. She covered it up by putting her hands over her face.