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: physical property 
Words: obese, fat, vitamin c, heavy, thin
vitamin c

Category: emotional status 
Words: down, emotional state, loveful, ashamed, flat
flat

Category: chocolate food 
Words: fudge, heavy, smear, rich, chocolate cake

smear