Visible crew/equipment: Early in the episode a thumb/finger is visible at the bottom of the screen turning the timer wheel simulating a working timer that is actually just a dummy prop, a few seconds before it explodes. (00:02:39)
MacGyver (1985)
1 visible crew/equipment mistake in Pirates
Starring: Dana Elcar, Richard Dean Anderson
Continuity mistake: During the car chase through the desert, the rear view mirrors on both cars disappear and reappear repeatedly.
The Eraser - S2-E2
MacGyver: Look, if this works, it'll keep us from gettin' caught. If it doesn't, it'll keep us from gettin' old.
More questions & answers from MacGyver
Answer: Late one night, Geoffrey used a covert listening device to overhear David explaining his barricade device to Janet which is how he figured it out.
How do we know Geoffrey really did use a covert listening device? They didn't mention him using one.
There was a scene of him using it when David told Janet about his barricade.