Continuity mistake: After getting off the school bus, when Gus falls into the hole that Sam has dug in front of the school, he's wearing his watch as usual. As Gus sits up, his watch vanishes mid-shot; then it reappears on his wrist.
Continuity mistake: After Upside-Down Girl tells TJ he must do something about Dave, when the gang look for Sam and discuss the situation with him, the clock over the school doors repeatedly changes time between shots. Then, when Sam grabs the shovel and jumps back into the hole, the two hands of the clock vanish, only to reappear and change time yet again.
Continuity mistake: The gang hatches a plan and tells Dave that Sam is trapped in a cave-in, so Dave begins digging to save him. When Sam and Spinelli return with their ice cream cones, Sam's gloves vanish and reappear a couple of times while he is holding his ice cream.
Continuity mistake: After it is explained that without Dave, Sam is unfocused, you see that he has dug holes just about everywhere. However, after that scene, all the holes disappear.