In the episode A camping we will go,Jack tells Larry that he is going to go for a swim in the lake alongside the cabin. Hence, there should be water. However, when Larry comes to check on Jack later, watch the scene closely. There is no sign of a lake. There is just a big rock in which John Ritter is hiding behind, you an even see his hand sticking out as he is pretending to be taking a swim. The sound effects that they make of water trickling down a waterfall sound pretty fake. And then when Jack walks out of the lake(comes from behind the rock), his hair isn't even wet! You can take a swim without your hair getting wet, but to make it look more real, they could of at least made his hair wet! You can tell that the whole scene was fake, as with a lot of their props on that episode.