Bullfrogs were first described in 1802 by George Shaw. Shaw described the bullfrog in his book "General Zoology or Systematic Natural History". A bullfrogs call is a slow deep "g-r-r-u-u-u-u-m". Young bullfrogs will make a high pitch chirp before going in the water. Bullfrogs have toxic skin, though it is not harmful to humans. The toxins make it less likely that other animals will eat them.