Dogs are known as friendly, tail-wagging creatures that will do almost anything to please their owner. However, every animal can act out when it's scared or placed in an unfamiliar environment.
Foster Wong, a certified professional dog trainer from the American Karen Pryor Academy, provides insights on how to handle a canine that suddenly turns aggressive.
'Aggressive behaviour in dogs is very common. It's definitely one of the top five issues owners have, on top of other issues like pulling on the leash, toilet training and barking,' says Wong, who practices positive training methods. 'The reason for aggression - lunging, growling and biting - is that dogs are acting out of fear.'
As aggression can be classified into different areas, such as dominant, possessive and maternal, Wong sees fear as the most common type. One example, he says, involves dogs that are not used to children running around and shouting.
'Some parents don't realise there's an issue with the dog and let the children say 'hello'. But if the dog is on a leash, it has no way to escape,' Wong says. 'In these kinds of situations they want to fight or [take] flight. Every dog has its comfort zone of personal space and if you burst their comfort bubble, the dog will react. Sometimes the only thing they can do is bite.'
Another factor on whether a dog will become aggressive depends on a particular situation. Wong gives an analogy of personal space for people. If you are sitting on a bus that is crowded, and a person sits next to you, most people wouldn't react. However, if the bus were empty and a person takes the seat right next to you, it would feel awkward and strange.
Wong says: 'Dogs don't always act out. It depends on the context. Your dog may be OK with John, but not OK with kids in the park.'