What do cockroach droppings look like?
It looks like black pepper. Like if you accidentally spilled some from your pepper shaker. Very small and black.
I think the best way to put this is that their size depends on the size of the frog, but they are black or brown, smelly and contain indigestible insect parts, eg. moth wings, beetle shells, grasshopper legs. They look like little rocks but if you look at them closely you can tell that there frog droppings :)