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: boxing terminology 
Words: ring, lifeline, jab, deck, knockout
lifeline

Category: animal 
Words: train, fly, jump, leap, grasshopper
train

Category: aesthetic characteristic 
Words: bright, fine, pretty, penalty, attractive

penalty