This scene is pretty much the basis for the metaplot that Ferris and Sloane are psychological projections of Cameron and that he’s really just absolutely insane.
He’s licking the glass and making obscene gestures with his hands.
John Hughes’ commentary: The closer he looks at the child, the less he sees…The more he looks at it, there’s nothing there and I think he fears that the more you look at him, the less you see there isn’t anything there. That’s him.
Ferris Bueller’s Day Off
Considering why Charlie Sheen’s in the news right now, I thought this was appropriate.