Monster is the name that the clan cats use to describe a car, truck, etc. They call them monsters because they are afraid of them. They often think that they are alive or want to chase them. They some times call boats "water monsters" because they are monsters on the water. The cats seem to think that the monsters "swallow" the twolegs. They also notice how they only go on Thunderpaths (roads). The clan cats don't like monsters because sometimes their clanmates are hit by them and injured (like Cinderpelt) and often killed (like Snowfur). In a chat on of the authors said if she were to change the name of one thing in the warriors series it would be monster because she "abselutely hates that!" It was also stated in a chat with the authors that the clan cats will never understand what monsters and thunderpaths really are.