[header] How to choose a jack russell puppy [title] Know the personality of the jack russell terrier. [step] You should know what you will be getting into when you decide to adopt a jack russell, to make sure the breed and your lifestyle are suitably matched. [substeps] Jack russell terriers tend to believe they are a lot bigger than they actually are. 
This means that they may tend to take on dogs that are bigger than them. Jack russells can be more prone to aggression than other breeds because instinctively they attack, rather than back down, when frightened.