Yep, I saw that too. It's that vapor effect that happens around aircraft at speed under certain conditions of pressure and temperature. It's commonly associated with breaking the sound barrier, though that's not exactly always true. It's got a name that I can never remember.
Ah... that’s it... the Prandtl-Glauert singularity:
http://en.wikipedia.org/wiki/Prandtl-Glauert_singularity
I can never remember that name.