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He touched the ground in between barrel rolls. Watch again, the back of the Piranha goes off the screen and just lightly touches the ground.

It's impossible per the game code to do two BRs in one jump. If you don't believe that, go ahead and try on Ubermall on the long straight. Boost when coming up the hill, do a BR and try to do a second one.

It's swell to chain BRs like that but it's lying to say you can do two rolls in one jump. As I said, just try it on a very long jump in the air, try to do two barrel rolls during that long jump.

Have fun.