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: type of rigidity 
Words: solid, leverage, hard, unbending, firm
leverage

Category: food 
Words: sausage, frank, loyalty, cheese, pork
loyalty

Category: emotional status 
Words: emotional, fret, bored, frustrated, headstock

headstock