Miley Cyrus -- She Can't Stop ... Spitting on the Crowd

Mystery solved: Miley Cyrus is a spitter.

Miley added a water sports element to her concert Thursday night -- taking giant gulps of water and spitting it back out ... all over the audience.

She pulled the stunt several times and even more baffling … is the fact the audience seemed to like it.

If Katy Perry was worried by a quick peck, imagine what would have happened if Miley pulled this on her.