At around 18 min Ira Messing leaves Walter while moving a pawn on the chess board in the wrong direction. In addition, when Leo leaves the room a few seconds later, Walter switched from the counter playing chess to a table examining the high heel.
Walter's chess board is set up incorrectly. The white king and queen are swapped from their correct positions, and given the position of the other pieces on the board, it would not be the result of having moved during gameplay.
When Therese tells Walter that she's a party girl, not a prostitute, she says the distinction is a matter of semiotics. Semiotics has to do with signs and symbols and their meaning, not with that of words and terminology. The term she should have used instead is semantics.