Glow in the Dark Drool
Glowing ice melts. If it melts in your mouth, the result is glowing drool. Tonic water isn’t all that tasty, so assuming you don’t want to swallow the melted ice, you can get glowing spit or, as David learned, you can make whatever you spit on glow. Less-nasty applications would include making the water in your bathtub or pool glow. It’s hard to see a glowing ice cube in your own mouth, but that problem is easily solved if you have a mirror handy.