Continuity mistake: When Karen arrives at work, she places her bags on the chair, and then puts them down onto the floor. In a following shot they are back on the chair, then in another shot they're gone again.
Continuity mistake: Before Fannie starts the photo shoot with Will and Grace, she unbuttons the top of Grace's trousers. But later on in the shoot you can see they're done up, then later on they're undone once again.
Continuity mistake: When Will runs in and takes a photo of Matt Damon and Grace kissing, to get evidence Matt is straight, when Jack pulls out the film from his camera, two boxes (a black and red one) vanish from the coffee table.
Continuity mistake: When Will and Grace fight over the birthday cake which Larry holds, it results in the cake being dropped. Note the position of the cake after it is dropped to the floor. In a later shot during their conversation, it has changed.
Continuity mistake: When Jack is making his film for Karen, as he's interviewing Grace, he holds a cheque book up to his mouth. Between shots the book randomly alternates from being in his right/left hand.
Continuity mistake: When Jack is talking to the board manager about kicking Will out of the 'Subway Tush' invention, confetti on Jack's shirt front disappears then reappears, and the confetti on his shoulders differs as well.
Continuity mistake: When Will tosses all the ties out of his cupboard, the tie which landed on the end of his bed keeps changing. In some shots it's a blue and black stripy tie, in others it's a yellow and brown stripy tie.
Plot hole: In this episode, Will says that he "never saw himself as a dog person." But in a later episode, the one where he sees the psychic, he talks about how he had a dog when he was little and how much he loved the dog.
Continuity mistake: Grace walks into her office to see that she has a vase of red roses from Leo. During her conversation with Karen about Leo, and during their kiss, the position of the roses sticking out at the top of the bunch changes.
Continuity mistake: When Grace and Leo accidentally meet each other in their apartment, ruining Will's surprise, they have a cuddle, then Leo walks over to the fridge. Between shots the back of his collar changes from folded down to folded up.
Visible crew/equipment: When Jack is telling Will he's so happy he's going to help him with his new product, they are standing in front of a painting. As Will stands up, you can see a cameraman reflected in the glass.