Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.

Category: aesthetic characteristic 
Words: mild, fair, texture, even, milky
mild

Category: employment activity 
Words: pay, instruct, heat, fire, scold
heat

Category: animals 
Words: dog, duck, swim, horse, cat

swim