My guess is that there's a hole in the balloon at the end that she puts in her mouth, possibly covered with tape. In any case, the air is let out of the balloon as it's pushed into her mouth and eventually escapes through her nose. These balloons deflate by collapsing lengthwise, so it would be perfect for this type of trick.
Old, but i can't stop watching it. :lol
Edit: i keep watching and it sounds like i hear air escaping. It's also kinda odd that the balloon's not fully inflated.
