One of the buildings at Gawbridge Mill, which is located on the River Parrett and on the road between Coat and East Lambrook, has a round hole about 4 feet of the ground, which was built into the brick wall when it was originally constructed. According to Curious Somerset by Derek Warren it is an access hole for cats, so that they could get inside the mill and kill any rats or mice. However the rats and mice were unable to climb up the wall to get in through the hole. That sounds very plausible, although I cannot find any mention anywhere else of such "cat holes". I cannot think of another purpose for the hole and the bottom edges clearly look worn. Apparently it was more common to cut cat access holes in the wooden doors of mills. The current Gawbridge Mill, which was powered by water from the River Parrett, dates from the 18th century. It was in use as a mill until the 1960s.
The cat hole is clearly visible from the public road. I zoomed in with my camera to take the photograph from the road. Grid reference: ST 443 196