Continuity mistake: In the opening scenes, Grace has red nail polish on. Later in the same scene, it has vanished as she shakes Mrs. McFarland's hand. (01:03:20 - 01:06:15)
Plot hole: Ellen and Rob wear wedding rings, yet their wedding is not announced until "An Affair to Forget" in the second season.
Lows in the Mid-Eighties (1) - S3-E8
Plot hole: In this episode during the flashback scenes, it is shown to us that Will comes out of the closet during his freshmen year of college during Thanksgiving Break, when they spend the weekend at Grace's Parents house. However in the season 1 episode "William, Tell" Grace claims that Will came out to her at senior year of college during Christmas Break. Quite a difference for such a memorable time.
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)
Continuity mistake: When Grace finally decides to move into Will's apartment near the end, we see Will eating a tub of ice cream. Between shots the ice cream tub lid jumps from being on the table behind Will, to suddenly sitting right in front of him. (00:42:00)
Lows in the Mid-Eighties (1) - S3-E8
Revealing mistake: At the party it is obvious none of the red plastic cups have drink in them. (00:45:00)
Continuity mistake: When Grace is telling Will about his dad's affair, she mentions that he grabbed the other woman's ass when she brought him a packet of Goobers during the interval. The thing is, she sees them for the first time during the interval, and we see the conversation that follows. The mistress brings him wine, not Goobers, and he doesn't grab her ass.
Plot hole: The apartment block where Will lives supposedly has the same layout for each floor of the building. Yet in "Yours, Mine or Ours" the room 12D is seen as located right in front of the elevator, the same location as Will's apartment door - however Will's apartment is always seen as 9C.
Went to a Garden Potty - S4-E20
Continuity mistake: When Karen is talking with Norman about donating funds for his advert, and then when Jack enters, between shots during the scene Karen's pearl necklace keeps jumping in and out of her black shirt. (00:45:00)
...And the Horse He Rode in On - S5-E1
Continuity mistake: When Grace and Leo are speaking at the table in the coffee shop, the muffin on the table keeps changing position, and Grace's hand keep jumping on and off of it between shots. The bites taken from it also differ.
Lows in the Mid-Eighties (1) - S3-E8
Continuity mistake: When Ellen says to Grace "Okay, what do you mean Will and You have never done it?" the red plastic cup she holds swaps hand three times between shots. (00:45:25)
Revealing mistake: After the opening credits there is a shot showing the house on the island where Karen and Stan live. If you look at the hanging chair, you can see that Karen is sitting in it. But in the very next shot she is in a meeting with Will, in a different outfit. This is a re-used shot from the previous season, which shouldn't be there. (00:04:20)
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)
...And the Horse He Rode in On - S5-E1
Continuity mistake: While in the coffee shop, Leo writes Grace a prescription. As she is reading the piece of paper, Leo puts the prescription pad back into his shirt pocket. In the next shot the pad is on the table in front of him.
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.
Answer: A history of the game can be found at http://www.fast-rewind.com/bacon.htm.
J I Cohen