When Daphne (Jane Leeves) and Niles (David Hyde Pierce) are in the bedroom talking, there's a moment when they both go to lock all the doors in the room. The door that Niles locks from the hallway, the main door, is like the other doors in the room in that it locks from the inside. Yet Niles opens the door and locks it from the outside.
Donny orders a "Scotch, rocks", but the bartender pours a drink from a bottle of Crown Royal, which is a Canadian whisky, and not Scotch. (It appears to be the same prop as appears in Frasier's apartment in the previous episode.)