Mammals
A variety of frogs eat small mammals such as mice and small rats. African bullfrogs (also known as pixie frogs) are capable of swallowing small rats whole. Ornate horned frogs (also known as Pacman frogs) consume small mice and pinkies in captivity and other small mammals in the wild. Frogs will eat whatever small mammal they can fit in their mouths provided that they are significantly larger than it.
Fish
Aquatic frogs will eat small fish if they manage to catch them. Guppies, minnows and goldfish are all possible prey items for frogs in captivity. They eat the fish the way they eat their other food: by catching it in their mouths and swallowing it whole.
Other Frogs and Lizards
Many frogs will even eat their own kind. A small frog is always a potential meal for a larger frog, which is why the size of your frogs should always match if keeping more than one in the same enclosure. They will also not hesitate to feast on small lizards that happen to be walking by.
Birds
Some frogs have been reported to consume small birds. Limnonectes megastomias, also known as the fanged frog, was discovered in Thailand in 2009. These frogs reportedly sit by rivers or streams and wait for birds to land or pass by, wherein the frog will capture them with its tongue and swallow them whole.