Plot hole: Ellen and Rob wear wedding rings, yet their wedding is not announced until "An Affair to Forget" in the second season.
Continuity mistake: When Karen is sorting out her clothes at her work desk, the black sweater hanging over the desk lamp disappears then reappears. (00:26:40)
Visible crew/equipment: When Karen offers her hand to Jack when they first meet, you can see the boom mike at the top of the shot. (00:37:25)
The Unsinkable Mommy Adler - S1-E13
Continuity mistake: When Grace is reading through her diaries, through all following shots in the scene the position / location of the yellow, furry diary on the floor keeps changing. (00:37:40)
Brothers, A Love Story - S3-E14
Continuity mistake: When Karen reads Stan's will and sees that a third of his money will go to charity, she goes woozy in her chair. In this shot the table is free from loose jewels, yet in the next shot two rings are sitting on the table. (00:10:45)
Boo! Humbug - S1-E5
Continuity mistake: At the end of the episode, "Buzzy Wuzzy" takes her bee mask with her and they leave. But when Will and Grace dive for the jawbreaker, the bee mask is back on the coffee table. (01:01:25)
Continuity mistake: When Grace gets out all the videos which hint Will's 'secret', she puts the bag on the table, but in the next shot it's in her hand. Between these same shots a sticker also appears on one of the video cases. (00:29:50)
Continuity mistake: When eating in Will's office, Grace eats salad from a plastic container. Through the scene the salad in the container changes colour, position etc. Also between shots, lettuce appears on Grace's fork. (00:28:05)
Continuity mistake: When Karen pours a cup of coffee, the coffee is old, so she pours the coffee out of the window and puts the blue mug in a large see-thru plastic container. In the next shot the mug has vanished. (00:10:45)
Visible crew/equipment: When Karen stands by the pillar she says "I want to talk to Ja...Wi...Rosario" and as she does, Jack and Will step forward. Anyway, you can see two white tape markers on the floor which they stop at. (01:13:50)
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)
Acting Out - S2-E14
Continuity mistake: When Grace is talking to Karen on the phone, asking for advice on how to be mean, Karen is in the bath. The amount of bubbly foam on her arm differs in every shot. (00:11:40)
Tea and a Total Lack of Sympathy - S2-E10
Continuity mistake: After Jack and Grace burst through the paper screens at the 'Antiques on the Road' show, the hole made in the screen changes between shots. (00:34:30)
Continuity mistake: When Will and Grace sit on the rocks in the meditation room, at the end of the episode, the position of Grace's coat changes between each shot. (01:22:00)
Whose Mom is It Anyway? - S2-E4
Continuity mistake: When Jack and Karen are waiting outside the INS office,Karen's leans against the back of the bench she is sitting on, and her arms are not crossed. When the shot changes, her arms are suddenly crossed. (00:12:15)
Will on Ice - S1-E11
Continuity mistake: When Will and Grace play the "love her, hate him" game, they open a magazine up. In the next shot you can tell it's on a different page, because the layouts have changed. (00:05:45)
Continuity mistake: When Will introduces Grace to April, the pencils in Grace's hair changes between shots.