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: fire, hire, ground, pay, retire
ground

Category: consumer product 
Words: joyful, program, activity, food, content
joyful

Category: animal 
Words: wave, cockroach, dangle, fly, jump

wave