Oh god....um, One is a feline and the other is a rodent.
Richard Mumford's method of categorizing rope techniques. CAT stands for Climber Anchored Technique. RAT stands for Remote Anchor Technique. In thinking about the techniques in this way it really helps in understanding the mechanical advantage nuances and all that. Actually makes a lot of sense. Here is a thread on it: https://www.treebuzz.com/forum/threads/rat-cat-and-mcat.41135/