What is the strange phenomenon above this explosion on Mythbusters?

[martix]

Here's an explosion from mythbusters.
At about the 1:35-36 mark, there is a particular camera angle where if you go frame by frame, just as the explosion starts, there is a weird disconnected phenomenon right above the explosion(kinda like a cone).

Could anyone explain what that is?
A camera artifact?
A mach disk-like phenomenon?
Something else?

 

[russ_watters]

Because of the symmetry, I'm thinking it is an internal reflection in the lens of the camera.