They cut the legs off with a sharp curved blade
Where I'm from (a supplier of places that eat them) apparently they used scissors.... there was a newspaper story on those in the local frog industry that caused a bit of an uproar....
Several months ago, at a dinner I had been invited to by several Chinese people, I tried one of the dishes and the eyes of those sitting next to me lit up..."Do you know what that is?" they asked, clearly delighted..... "Frogs"
It was... okay.... the Chinese there said the dishes very very authentic and I didn't recognize most of them (conceptually the weirdest were flat noodles that looked like tagliatelle but made of tofu....). Mostly there were bowls with solids suspended in sauce, the chinese plucked out the solids and mostly ignored the sauces.