From Halopedia, the Halo wiki
A gatt is a small creature native to Sanghelios. These animals are apparent visitors to Sangheili barns and are possibly a kind of farmland vermin, like insects or rodents. They are known to be trapped and preyed upon by a predatory animal called the terret, which likely serves as a natural deterrent against the gatt.
List of appearances
- Halo: Outcasts (First mentioned)
- Halo: Outcasts, chapter 1