The Bermuda Triangle Crisis - S2-E4
Revealing mistake: When Wonder Woman drops a mine into the water, she's supposed to be dropping it into the ocean. However, you can see a drain plug of some sort in the background and the "ocean" is obviously a pool, or similar.
One of Our Angels is Missing - S4-E16
Revealing mistake: Fake backgrounds and stuntmen are extremely evident throughout the entire episode.
Revealing mistake: The opening scene was shot twice, complete with a rear-end automobile collision in the foreground for both takes. The initial collision destroyed the taillights of the first car and the headlights of the second car and ruptured the second car's radiator on impact, spilling its contents into the street. The production crew attempted to sweep away the debris with a broom before the scene was reshot. If you examine the roadway before the two cars appear in this scene, you will see a prominent splatter on the pavement that has been swept with a broom almost precisely where the cars impact again moments later.
Revealing mistake: Jamie prepares to split a giant heavy log in two, with her bionic arm, so that it will fit into her fireplace. Just as her arm comes down, you can see the middle seam where the log was pre-cut for the shot, so that it easily breaks in two. (00:00:30)