John was next.

He prepared an ordinary drinking glass.

Preparing to color his mouth.

For John's turn, I wanted to make sure our test would work.

I gave him directions; "Don't try to not backwash".

He dumped the red Kool-Aid powder into his mouth, and took a sip from the water glass. It worked! His red spit went right back into his drink! 

It was a nice cloud of red, quickly spreading throughout his drink. Ugh!

John made it look easy. He was ready to try another one. 

Everyone was heckling him for his reckless backwashing, and he was eager to redeem himself.

Meanwhile, a layer of backwash-tainted fluid now sat at the bottom of his glass.

Amy was next. She looked thirsty. 

Thirsty for science!