If a word conforms to a special rule, I call it a Mutated Word™.
Use the examples below to find the rule.
|Mutated Words™||Not Mutated Words™|
In case you want it in CSV:
Mutated Words™,Not Mutated Words™ BRASH,CALM CROWN,TIARA DINNER,LUNCH FEEL,SENSE LADDER,STAIR SEAT,STOOL SUPPER,BREAKFAST THINK,REACT WHOSE,WHOM
The puzzle relies on the series' inbuilt assumption, that each word can be tested for whether it is a Mutated Word™ without relying on the other words.
These are not the only examples of Mutated Words™, many more exist.