Two comments are made about the gravy having a skin on it. However, the turkey is not yet out of the oven; gravy only forms a skin when it is made from animal fats.
During the food fight scene, to the right of the table, the wall with the fireplace can be seen wobbling.
When the guys are in the living room talking about family, Diane can be seen in the
window by the front door for approximately 8 seconds before ringing the doorbell.
At 11 mins in, just after Sam arrives and spins the television around, the shadows of filming equipment can be seen on the left of where Frasier is sitting.