Ghost Ship - S3-E4
Visible crew/equipment: MacGyver is repairing the broken boat to get to the abandoned ship. When he leaves the shore and starts to paddle towards the ship, you can see a boom mic drop into the picture from top left. (00:09:15)
Continuity mistake: MacGyver appears to be a novice at mountain climbing, but in the very first episode he mountain climbed like a professional.
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.