@cjd That liquid is adhesive. If you watch the video they even turn the glass upside down and it's still stuck to the bottom of the glass.

https://www.youtube.com/embed/YY80QLee_vc?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent