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: animal 
Words: flutter, swim, ant, fly, bats
flutter

Category: physical activity 
Words: drop, fall, leaves, bend, exercise
leaves

Category: consumer product 
Words: thing, activity, disappointed, content, substance

disappointed