When geese feel threatened or cornered, they may exhibit defensive behaviours to protect themselves and their territory. Hissing is one of these behaviours. It's a vocalization that geese use to communicate their unease and to establish boundaries.
The hissing sound itself is created by the expulsion of air through their beaks. Geese might raise their necks, spread their wings slightly, and open their bills while emitting this hissing sound. This display serves as a warning to potential threats, such as humans or other animals, that they are feeling threatened and are prepared to defend themselves if necessary.
Geese are naturally protective of their nests, mates, and young goslings. By hissing and displaying aggressive body language, they attempt to deter perceived dangers and maintain their safety. It's important for humans and other animals to respect these warning signals and give geese the space they need to feel secure.