Continuity mistake: When Will is cleaning the tray, and in all following shots, from when he leaves the room, to when Karen walks over to Grace, to tell her to go get Campbell, there is a wine bottle which keeps jumping from the edge of the blue sink counter, to the edge of the counter which has the cooking gas-hobs on it. (00:09:55)
Continuity mistake: When Will is standing cleaning a tray, on the counter behind him there is a large circular wooden board, with a white tea-towel sitting on it. After he cleans the tray and walks off, the white tea-towel has moved off the wooden board, and is on the edge of the counter. (00:09:55)
Continuity mistake: As Grace and Campbell kiss on the couch, Will returns to the cabin and then Grace shuts Campbell outside. The edge of a rug with tassels is sometimes draped over the back of the couch in some shots, and isn't there in others. (00:15:25)
Continuity mistake: When Val is folding her towels in the laundry room, she completely folds up a towel as Will enters the room. Then she is seen re-folding the same beige colored towel. Then, though she had picked up the beige one, she is seen setting a dark towel on the stack. (00:25:45)
Continuity mistake: When Karen is sitting at her desk, she says "get out, already," and she has one bottle of nail varnish in her hand, and there are bottles on the desk in front of her. In the next shot she holds about four bottles in her hand, and now the bottles on the desk in front of her are differently positioned. (00:29:25)
Revealing mistake: When Grace is getting out the Board Games for her and Karen to play, the names of the Board Games have been covered with strips of tape. (00:53:00)
Continuity mistake: When Karen enters the apartment, the position of the board game boxes on the table change, especially the long white board game box which just out and back into a stack. (00:55:05)
Continuity mistake: When Karen is lying on the table, her jacket is unbuttoned. And when Jack pushes her off the table and she gets back up, it's still unbuttoned. But as the shot cuts to her heading quickly over to the door, her jacket is now buttoned, but there was no time for her to do it.
Visible crew/equipment: When Jack is explaining to Will how to visualize someone else while kissing them, you can briefly see a blue mat in the bottom right corner of the screen. This is where Karen later faints. (00:11:55)
Continuity mistake: After Grace tells Will he has to go on a second date with Nathan, she runs out onto the terrace to hide. When she comes back into the kitchen, she leaves the terrace door open. In the next shot it's closed, the open again. (00:16:40)
Alley Cats - S1-E21
Continuity mistake: Grace unpacks her Scrabble board game from her bag, and puts it on the table, and puts the bag on the floor. Then her friends tell her she is too competitive, so she goes to her bedroom. As she goes, you can see that the board game on the table has now been replaced by the big red bag. (01:10:05 - 01:11:55)
Alley Cats - S1-E21
Plot hole: When they are bowling and Grace is losing, she says she's fine with it and she knows how it feels to be her middle sister, then Will reminds her that she's actually, "The baby of the family looking for Daddy's approval." However, in all later episodes, Grace is portrayed as the middle child with a younger sister, Joyce and an older one called Janice. This mistake is made in a few other places through the show, where Grace either refers to how old she is (youngest, middle child etc) incorrectly.
Alley Cats - S1-E21
Continuity mistake: When Rob & Ellen are confronting Grace about how competitive she is, there are several shots of them from the same angle. In some shots there is a red bag visible in the bottom left corner, in others it disappears.
Alley Cats - S1-E21
Revealing mistake: When Will goes to pour himself a glass of whiskey, the brown liquid that is chosen to represent the liquor has foam bubbles on the top of it that resemble the ones that soda has.
Alley Cats - S1-E21
Plot hole: In the bowling alley scene, Ellen states that Grace would need to knock down 27 pins in order to tie. Will and Grace then have a conversation, and Grace gets a strike with her next ball. They then start gloating that they have beaten Rob and Ellen, but the scores don't add up, and they couldn't go into the lead on that round.
Guess Who's Not Coming to Dinner - S2-E1
Revealing mistake: When Will is supposedly naked, reading his book, you can see he is wearing underwear when he slams the book down as Grace leaves. (00:08:30)
