The Puppy Episode (1) - S4-E22
Continuity mistake: In the scene where Ellen goes to Susan's room after Richard makes a pass at her, she has her jacket in her hand when she enters the room. When Ellen leaves the room hurriedly, she leaves without her jacket, but when she is in the hallway about to go back to Richard's room, she has her jacket in her hand.
Answer: This groundbreaking episode was in the fourth season, episodes 22 and 23.
Jason Feng