They are fearless. Mine attacked a Great Dane because it came into the yard. Attacked as in running under the dog and jumping to try and bite the belly of this animal that was 10 times bigger. Funniest thing watching the Great Dane duck walking down the road as it was trying to get away from the miniature terror.I've had a lot of JRTs and "timid" and "fear" don't enter their decision making process.