The coke can on top of the fridge both disappears and reappears during several shots.
In this episode the cupboard above the fridge has no doors, but in the episode Bomb (1982) it does have doors.
Rick's buttons change during scenes.
There is a small fire at the end of Rik's bed, which Mike uses to light a cigarette, however the view changes to Mike and Neil when Neil mentions he doesn't like sharks but when the view changes back to all four of them, the fire has gone.
Though the coinbox is there the wall telephone is missing at the at the start but appears during the sofa scene. There it remains until ripped from the wall by Vyvyan much later on.
When the threesome enter Rick's room, smoke is coming out of Rick's door. But when they go in, there is no sign of smoke in the room.
After Mr. Balowski drinks the potion and becomes an axe-wielding homicidal maniac he corners the boys in Neil's room and as he begins hacking his way in a la "The Shining". When the camera switches angles you can plainly see that the panel he's chopping his way through is different than the other ones, it's made of a thin balsa wood that easily breaks apart when he hits it. It also explains why he continues to focus his chopping on that one panel even when there's not much left of it.
When Vivian leaves the land of Narnia. Vivian's mouth doesn't move when Vivian screams as he slides down a dark tunnel when he enters a tree in the land of Narnia.