Revealing mistake: When Jamie sits down after rappelling down the canyon wall you can see that he has climbing rope attached to his harness. It's wrapped in duct tape to look like its the rope he and Adam made of duct tape. This may just be a safety line to support his weight if he duct tape rope snaps, but the Mythbusters usually point out any backup safety systems and explain that they are there for caution and don't contribute to the test. (This was explained in the aftershow. It was a safety line required by the shows insurers).
MythBusters (2003)
Episode list - season 13
Starring: Adam Savage, Jamie Hyneman, Kari Byron, Robert Lee
Genres: Documentary, Mystery
More mistakes in MythBusters
Adam: Am I missing an eyebrow?
Seasickness: Kill or Cure - S3-E24
Question: Why does a separated bubble form when you drive with your tailgate up?
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Answer: A more complex and complete answer probably isn't possible here, since we're dealing with fluid dynamics, pressure, boundary levels, etc. A simply answer would the air in the bed is kept there by the fast moving air coming off the roof of the cab. If there was no "secondary bubble" of air, you would have a vacuum in the bed. When air comes off the roof, it needs a place to touch down, which it is able to do with the top of the tailgate. The fast flowing air moving over the bed keeps the air that's already inside the bed from "escaping." However, the air in the bed is still moving and creates a vortex in the bed, which is described as a bubble. When the tailgate is down, the air coming off the roof will gather at the back of the cab and create drag.
Bishop73