In the episode where Arnold and Gerald are recording these two guys at the back of the van who look like they are up to no good, you will notice that Gerald stops recording once in a while so that he can talk to Arnold. Look for the part where the two guys are holding gas canisters, you notice Gerald is asking Arnold about the gas and he is not recording, infact his camera is off to the side of him. But yet later when they play the tape it shows the two guys with the gas canisters.