These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
More specifically, after someone mentioned in a comment on that strip that Autumn's ears change with her expressions, one person replied that "she has mood ears." Since then, the phrase has been in the comments of nearly every strip involving a very expressive Autumn.