The Puppy Episode (1) - S4-E22
Continuity mistake: When Ellen tells her friends that she is gay, she starts to digress. There is a bunch of wine glasses on the counter directly behind her. In several shots of the friends around the table, there are no glasses to be seen, but when Audrey says "I thought you had something important to tell us", she is holding a glass of wine. When you next see Ellen, the glasses are no longer on the counter, and the glasses are actually on the coffee table a moment later when the friends get up to leave. Yet no one actually served the wine out or got up to get any from the counter.
Answer: This groundbreaking episode was in the fourth season, episodes 22 and 23.
Jason Feng