Jamie: Aren't tracer rounds illegal?
Adam: How hard can it be to blow up a room full of gasoline?
Adam: Hell or high water we are gonna get him back out! We leave no man behind on MythBusters man.
Adam: Jamie, marinade.
Adam: We got a robot in the water, he's stuffed with tuna and it's just another day here at Mythbusters.
Jamie: When will the fun ever stop?
Salvatore: Mmmmmm... Yummy.
Jamie: I always enjoy seeing Adam in pain.
Adam: Am I missing an eyebrow?
Adam: I wouldn't say Jamie's an evil genius.
Jamie: Give it your best shot! Come on.
Scottie: Maybe it's a myth that methane is flammable.
Adam: It's not a myth. We're just idiots.
Adam: If I had any dignity, that would have been humiliating.
Adam: Do you actually have moods?
Jamie: No.
Jamie: What's the problem, you don't believe the math?
Narrator: Adam and Jamie have never been afraid of going deep.
Jamie: Well, that's a bright light you got going there, buddy.
Jamie: I think that was one of the most destructive things I've ever done. That was cool.
Jamie: Adam, the police officer says you need to drink more.
Adam: I'm not doing anything the Pakish wouldn't have done if they'd had a chainsaw.
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