Listen for a soft growling. And the unicorn growls softly, very softly, so as not to frighten them. The crowd gapes with wonder. -- Peter Spielberg, Twiddledum Twaddledum (1974) A unicorn's extraordinary soft growling is oddly mesmerizing, like the purring of a guinea pig. The sound's hypnotic quality makes it difficult to pinpoint in space, however, even with state-of-the-art equipment. The dreamlike growl tends to smooth out and even obliterate other environmental sounds. The waveform of a unicorn's affectionate growling.