Audio problem: As Carlos is giving his speech at the barbecue, Julie sees Zach and says to Susan "Oh God". After cutting to a shot of Zach and his father it shows Julie and Susan again. If you look to the right of the shot you will see Carlos' face is just looking in front of him and not speaking, but you can still hear him giving his speech whilst he is in shot.
Continuity mistake: At the start of the episode, Zach picks up some gravel from beneath the lamppost and throws it at Julie's window. But when he leaves Susan the flowers, you can see that the gravel has disappeared.
Chosen answer: Poker. They have been playing that this whole time, once a week with everyone who was invited that lived on the Lane.