Sort of delayed, but I've had similar ventures with my Pacman frog. She will attack the tongs, completely miss the food, and then clamp up...it's a frustrating experience for both frog and keeper. I would still try to encourage the tongs, but maybe try different approaches for how you present the item. Are you feeding him during the day or night? Maybe try later at night, if it's possible, since that's when they'd be eating the most in the wild. If it happens again (and it definitely will) and he doesn't try taking the food again, take a break and try again in 20-30 minutes. I've found this to be helpful when my girl misses and gives up.