Colleagues and I discovered giraffe humming in three different zoo giraffe groups. The novel and important finding that this audible and low frequency vocalization was exclusively produced at night has altered our understanding of giraffe communication. It begs the question of whether giraffes are more talkative when their ability to perceive visual communication cues from other group members is limited. As the hum’s communicative function is uncertain, this provides a focus for more research on giraffe vocal communication. No follow-up research attempts were made to explore the functional relevance of auditory signals for giraffes to date.