Continuity mistake: When Jack sees the glue bottle it turns 180° between shots, check the position of the label. One could argue that both sides have a label, but a shot later the kid is grabbing the glue and there's no label on the side facing the camera.
Continuity mistake: When Jack is about to grab the remote control, check the pattern on the carpet: The position of the remote changes.
Continuity mistake: When baby Jack spills the glue, the stain changes its shape drastically between the first and immediate second shot.
Continuity mistake: When Greg tries to calm down the baby after showing him Elmo, the position of Jack's hands on the crib are not continuous between shots.
Continuity mistake: During the football game Bernard's sweat stains on the sweatshirt appear/disappear randomly.
Revealing mistake: After Bernard breaks the toilet Greg lifts up the baby. From the angle shot from behind, note the baby's fake hair and you'll notice he's been replaced for a very obvious dummy.
Continuity mistake: When Bernard Focker breaks the toilet and blue liquid spills all over, the baby's hairstyle swaps between the first and second shot.
Continuity mistake: Jack says "we have 23 minutes before they cut the cake". Next shot shows the dog and cat sharing a piece of cake. Next shot shows the cake not cut yet.
Revealing mistake: When LJ has his hands stuck to the bottle, you can see a material actually holding his hands on the bottle.
Continuity mistake: When Bernie is on the toilet, his feet go from wearing socks to no socks.
Answer: Muskrat is a "code word" they use to remind Jack to keep his temper under control.
Myridon