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: elements 
Words: ice, fire, burn, let go, combustion
let go

Category: animals 
Words: duck, jog, cat, pig, mallet
jog

Category: shady activities 
Words: unwarranted, replace, fudge, fib, cupcake

cupcake