Dogs are active by nature, and as pet parents, it's our job to make sure they get adequate amounts of exercise. (blog.petmeds.com)
They may become over-possessive and irritable when they don't get to play in open space or not given adequate amount of exercise to stimulate their mind, and that is when they start nipping people and other dogs. (lovelybordercollie.com)
Neutered male cats that do not get adequate amount of exercise are particularly at risk. (itchmo.com)