Leonard remarks Sheldon asks where they would all like to sit during a movie outing. The Arclight Theatre in Pasadena, CA is by reserve seating only.
In a close up of the bottom step in the hall (when Leonard is sitting on it), a white paint mark on the wood part of the step is visible, to the right-side of the carpet; this is also visible on the bottom step of the other floors, thereby confirming that they redressed the same set to show the different floors.
Leonard, sitting on a stair, says, "I've always been a people pleaser. Is that so bad? It's gotten me this far." Amy replies, "What, almost up four flights of stairs?" However, they live on the fourth floor, which is only three flights of stairs up from the lobby.
Sheldon is far too smart to ever miss-pronounce a word, but he pronounces "sherbet" as "sherbert".