- The spellings trog and trock are both used in the books.
The trogs (sometimes spelled trocks) are creatures like "rocks with teeth, given to infesting wells, dungeons, and latrines".
Dure had a flesh-eating trock apparently bound to him, which he kept hidden in his pocket. By accident or on purpose, it was dropped inside Higbert's clothes during a scythe-arms lesson. It irritated Higbert, maddening him and causing him to windmill his deadly blades.
Dure also used his trock to eat through the lock during the Winter War. It exudes acid that dissolves metal as well as flesh, allowing fragments to be collected by black articulated feelers, and shoved into the trock's mouth.