Goofs

Towards the end when Wally brings Sebastian home after his fight at the park, Cassy's apartment is on the ground floor of the building; but earlier on it was up a flight of stairs.

The garbage bags that Wally and Sebastian buy to dispose of all the lice-ridden items are a completely different style and color of the garbage bags they bought in the drugstore.

When Wally and Sebastian are walking through the park the woman jogging and the man on the bike with the beige jacket can both be seen crossing the camera twice in under 30 seconds. Without doubling back this is not possible.

On going to the drug store during the lice infestation they pick up black bin liners with yellow drawstrings. On returning home there is no sign of a yellow drawstring.

(at around 40 mins) When Wally walks into the bathroom drunk and looks at the fertility chart, his watch disappears from his right hand when his hand is on the door. It subsequently reappears.

Genetically, Sebastian couldn't be the child of Wally or Roland. Kassie has blue eyes, as do both male characters. Sebastian has brown eyes. Since blue eyes are a result of a double recessive gene, one of Sebastian's parents must have brown eyes.

This is an old myth. It is possible for two blue-eyed parents to have a brown-eyed child. Eye colour is not an exact science. They are other factors in play other than the old high school genetics lesson of BB, Bb and bb genes as this doesn't account for the obviously omitted green eyes.

During the climbing wall/birthday party scene, Roland and Sebastian are both on their own belay ropes when Roland goes up the wall to get Sebastian. When Roland is lowered to the ground, Sebastian's rope is no longer there. This is not a goof. When Roland starts lowering Sebastian, the end of Sebastian's rope can be seen dangling freely, implying that Roland unclipped him from his rope before lowering him to safety.

Towards the end of the movie at Sebastian's birthday party, in between scenes you can see Jennifer Aniston's ring switch from the right hand to her left hand. Along with Jason batemans hand, when he's outside by the grill, there is no ring but towards the end of the last scene, a ring appears.

At the beginning of the final barbecue scene, Wally is seen using a gas grill, as evident by the burner knobs. After walking in the house, he speaks of charcoal and lighter fluid, which are completely unnecessary when using a gas grill.