Hiccoughs, tourette's or an escaping demon?

I was reading a book riding the bus, sitting near the back. Behind me was a normal looking woman of about 40, and a normal looking young woman of about 19. A normal looking man of about 30 was sitting to my right and there were various other people scattered throughout the bus.

Suddenly, from behind me I heard a noise.

It sounded like someone with reverse hiccoughs yelling "BHEP!" while gasping. I turned around and the 40s woman was smiling. The young woman looked a little weirded out.

"BHEP!!!" yelled the 40s woman.

I turned back to my book.

overheard: on the #29