Any way to physically test a zapper??

I am on another Clark Forum , and someone is causing problems there stating that zappers are fraudulent- that they don't work. Is there any way to test one on an insect, or something VISUAL to PROVE that they do??? I tried holding a fly while zapping, and it didn't do anything but gross me out- since I HATE flies!! (they were maggots once you know!!! :-0 ) Anyway.... I was just curious about that- if anyone has ever been able to test it and killed anything visual, please let me know!
Thanks!
Tara Tweet