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: employment activity 
Words: recruit, replace, sack, heat, fire
heat

Category: emotional status 
Words: fret, truss rod, emotional upsets, sad, worried
truss rod

Category: direction 
Words: falling, backward, left, disgusted, down

disgusted