This frog with a perpetual frown isn't actually grumpy - that's just how the Black Rain Frog looks! This grouchy-faced amphibian has the most intimidating mug around. The proof is in the grumping. Scroll through for more grump.

The Black Rain Frog is a burrowing amphibian who is native to the Southern coast of Africa. One nifty characteristic possessed by this frog is that they burrow to create tunnels up to 150 mm deep.

In actuality, this frog isn't really crotchety. In fact, they're very considerate! One of their unusual mating season ritual occurs in the females of the species. The lady-frogs will secrete a special sticky substance from their backs, so that the male frogs don't fall off during the act of intercourse.

During mating season, the male frogs will actually stay in the burrow to guard their eggs and will send out little chirps as part of their calls.

(iSpot - Southern Africa)