When Jack is going out to his mom's, you can see Karen walk around the back of the couch and you can see her side step something back there. She is in a hurry to rejoin Will and Grace on the other side and it is really noticeable. When Jack's mom tells him that she doesn't know who his real father his, Jack then passes out behind the couch and we know it (the side-stepped item) was a mat for him to fall on.