In the opening sequence, the guys in the bar wonder whether an olive could float in beer, so Cliff drops an olive in Frasier's beer to find out. Norm says that the olive didn't float when the camera clearly shows the olive floats to the top.
In the final scene in Rebecca's office, as Sam and Rebecca get ready to kiss, the boom mic is moved from above them to the door, ahead of Robin's entrance. This is evident by the shadow of the mic and its boom very clearly cast on the wall behind Sam and Rebecca as it moves.