Right after the scene where they are climbing in between the walls and the Agent's hands have come through the walls to grab Neo, Morpheus yells and hten launches himself out of the wall to land on top of Agent Smith. Watch as they fall, because Agent Smith is not wearing his sunglasses! Then he is wearing them again when he says "The great Morpheus..." and THEN Morpheus head butts him, knocking his shades off.

(And watch Agent Smith's little head jerk to throw his own shades off as Morpheus connects. I'm sure Laurence Fishburne didn't REALLY hit him hard enough to kock his shades off... That's not really a slipup, just a little detail)