It's the Gay Pumpkin, Charlie Brown - S5-E5
Continuity mistake: When Leo comes into the apartment and starts talking to Will and Grace, they're sitting at the table. Grace has a newspaper which she holds over her plate. Between shots the newspaper keeps vanishing then reappearing.
Sex, Losers and Videotape - S5-E20
Continuity mistake: When Jack leaves his class to go talk to Grace, they are all sitting. As the angle changes we can see through the glass panel that they are all standing and talking to each other literally one second later.
Fagmalion Part Four: The Guy Who Loved Me - S5-E19
Continuity mistake: During the scenes with Will and Jack talking to Barry in Jack's apartment, the wine glasses, wine bottle, spoons in the salad bowl, tartlets, tray etc., change position and move about on the table between shots during their conversations.
Continuity mistake: After Will and Jack unwrap their breakfast, the pour some of the Smart Start cereal into their bowls, then put the box on the side. Between subsequent shots the box continuously alternates from having it's front / back facing us.
Women and Children First - S5-E17
Continuity mistake: When Jack and Sissy are sitting in his apartment, discussing what they've done with their lives, they both have mint cookies that they eat while they talk. The bites and size of their cookies, most noticeably Sissy's, change between shots.
Continuity mistake: When Leo and Will are at the expensive brunch buffet, Grace is telling Leo about getting food from the back tables of the buffet. Between shots the position of the items on the plate which Grace holds changes.
It's the Gay Pumpkin, Charlie Brown - S5-E5
Continuity mistake: When Will and Grace are on the biking trip with Leo, going to pick a pumpkin, during Will and Grace's conversation the scenery and background behind and around them keep alternating and changing between shots.
Fagmalion Part Four: The Guy Who Loved Me - S5-E19
Continuity mistake: When Will enters Barry's apartment with the big brown bag of Chinese food, he walks over to the chair and puts it down. On the table is a magazine laying parallel to a book. A shot later the magazine sits vertically to the book.
Continuity mistake: After Will and Jack unwrap their breakfast, Jack puts the wrapping that the Smart Start cereal box was wrapped in, on the table. In following shots the wrapping keeps changing position, from spread out, scrunched up, etc.
It's the Gay Pumpkin, Charlie Brown - S5-E5
Continuity mistake: In the scene where Grace is fixing her bike chain, there is black line going across her cheek. The shape and size of the line changes several different times.
Marry Me a Little More - S5-E9
Continuity mistake: When Jack is trying to prepare his wedding speech, he taps some wine glasses, which smash. He then puts them on the piano. In following shots the wine glasses, spilt wine and broken glass on the piano changes position / (dis)appears.
Continuity mistake: When Will and Grace are standing outside Will's apartment, after Grace arrives back from her honeymoon, Grace is holding a handful of photo envelopes. Between shots the way she holds these envelopes changes.
Marry Me a Little More - S5-E9
Continuity mistake: When Karen goes into the room to speak to Grace before she gets married, Karen's feather boa is on her shoulder, off her shoulder, on her shoulder...
Answer: A history of the game can be found at http://www.fast-rewind.com/bacon.htm.
J I Cohen