You study the gun and see that there is a "reverse" switch. "I might as well test it on on myself to see what it really does," you say, "I can reverse it if anything goes wrong."
You carefully aim it at the smallest part of your body you can think of: your fingernail. You pull the trigger and your nail becomes engulfed in green light.
As soon as the light fades, your finger starts to tingle. Your nail grows at a rapid rate, as if you haven't clipped it in months. The white slowly fades to yellow and you can feel years of dirt and grime cake themselves underneath. A long crack spreads down the center of yur stiff, yellow nail.
"Wow." you say, "that is truly disgusting."