During Will's fireside serenade, in one shot the capo on his guitar moves to much further up the neck.
During Jay's Australia monologue, the calendar behind his left shoulder, which is going up by a day each time a girl's head pops up from beneath the sheets, skips the 9th, when he is describing how he is woken up by a different girl each morning.
When Neil is swimming with the dolphins in Splash Planet, the zip on his wet suit changes places. In the close ups, it's at the top, and in the side shots it has been slightly pulled down. This is the same in subsequent shots.
When they are in the desert, they lean against the car; however, they are extremely dehydrated and sunburned and there is no way they could cope lying against the car, as it would be too heated.
When Simon is video calling Lucy in the internet café, the image of himself on the laptop screen is supposed to show the view from his webcam but is actually a completely different video recording: his head moves at different times, he speaks at different times and he seems to be in a completely different setting.
When the boys are stranded in the desert, the shadows from themselves and the car change position at random. When the car breaks down, the sun is almost directly overhead; later, it has moved in the direction the car is facing, and, as the boys all sit down alongside the car, the sun is once again high overhead.
When Will is on the water slide, Neil's waste is following right behind him. When Will reaches the bottom, there is a delay before the waste emerges, at force, to hit Will at force and smear over his face.
The waste was not going fast enough to hit him with that amount of force and it would have just sunk in the pool.