Looks like the bridle is photoshopped out to me... Otherwise, it looks like a loop of leather through the mouth and I can't see how that would allow for good communication since it would have to be pretty tight to not fall out of the mouth with nothing holding it up.
Doesn't look like anything is "holding" the bit in the mouth but her hanging on the mouth contact.
Thankfully, the bit resembles a rubber "dog bone" bit...at least sort of "soft" and "forgiving", but not used in those hands often!
I've seen people ride like this before or completely brideless and literally bitless...when done it was beautiful. Talk about communication!
It was a reining demonstration. I know the horse was ridden by Stacy Westfall at Congress in 2011...not only bridleless but no saddle either. http://www.youtube.com/watch?v=4YCgsZmjsww