Pierce is known for his distinctive voice and, like his "Frasier" co-star, Kelsey Grammer, is often called upon to provide voice work. His roles include the narrator of the movie "The Mating Habits of the Earthbound Human" in 1999, the walking stick insect "Slim" in "A Bug's Life", Dr. Delbert Doppler in Disney's film "Treasure Planet", and amphibian Abe Sapien in "Hellboy". Pierce declined to be credited for his "Hellboy" role because he felt it was the performance of Doug Jones, and not his own voice, which ultimately brought the character of Abe Sapien to life. He was the voice for "Drix", a cold pill, in the animated comedy "Osmosis Jones".