While Chandler is trying to tell Monica that he likes her, his hair is sometimes sticking through his hat and other times is smoothed out under his hat.
In one scene, Rachel's bra strap is falling, but the camera switches to Joey and it is no longer seen.
At the very end (right before the credits), when Monica rushes to hug Chandler, the sleeve of Courteney Cox fat suit can be seen on her right wrist.