What about reactive dogs that react because they want to fight with or play with the other dog?
Let's look at fighting. The generic dog would do a lot before it fought another dog, simply because injury=starve to death in a hunting animal. Therefore MOST fighting in the natural dog is spit and noise and the odd tuft of hair - posturing. Posturing is natural and normal but not what we want our dogs to do, mainly because of the reaction of the owners, and because a dog might get hurt by accident especially if there is a huge size difference. Before a fight ever kicks off, there is a lot of body-language that most humans miss - challenging, placatory, responding to the challenge and the placatory gestures.
(Some dogs, and especially b itches, fight for resources, and these fights mostly take place in the home. Once this kicks off, there is no going back, and the situation has to be remorselessly managed because at the whiff of an opportunity, these will be at each other with intent to kill. Such dogs can be any breed. There is not enough space for both of them. But this is in the home, not out and about meeting strange dogs and wanting to fight them).
But SOME dogs get a huge kick out of fighting. Let's look at those. Some are bred to fight. They may not have been fought for many generations, but the desire is still there, and the reward too. These breeds get a massive endorphin rush from fighting and killing: crucially, they are genetically programmed to ignore placatory behaviour, and if another dog submits to one of these, it may well still be attacked with intent to kill. Not all of these breeds are the obvious ones, but there are obvious ones. Not all of these dogs will ever want to fight, if carefully managed. IF the switch is thrown, however, this type of dog does not back down - it has been bred not to.
Some dogs (any breeds) have the endorphin rush from bullying, which is a step below fighting and can easily escalate to it. Dogs must therefore not be allowed to bully/intimidate others. Bullies are often cowards, which actually makes the behaviour worse, as once they have had a thrashing from another dog, they will be even more aroused when meeting strange dogs. Interestingly, when they meet the dog that bested them, they generally (not always) submit to it from quite a way off.
So - it is very important that your dog does not learn to love fighting, and does not get the chance to get a big boost out of bullying. Which means reading the situation and never letting it develop.
If your dog wants to fight or bully, it is not a bad dog - it is just being a dog.
Playing - let's look at play.
Playing in immature animals replicates natural behaviour. They practice everything that they would do as a normal adult - humping, chasing, fighting, pouncing - everything. As they get older, they only perform these behaviours in context. But oh! We humans - we want them to play seeing a fluffy Disneyfied round-the-circle happy with our little friends jolliness. And it ain't. It's competitive behaviour (think human sports - people get insanely serious about ritualised chasing, fighting etc). The dog that wants to play is trying to find out how fast, how far, how strong, how heavy - the other dog is. To check it out as a rival, not a chum.
Of course dogs can, will and do play nicely. They have special doggy friends that they love to meet and run around with. I love seeing my young dog run slowly so her terrier friend can catch her - then they swap and she chases him, and catches him very gently. That's okay.
But a dog lungeing at a strange dog "to play" doesn't want to "play" in the human nicey nicey sense - it wants to check that dog out for - how fast, how far, how strong, how heavy - the other dog is. To check it out as a rival, not a chum.
Which is why we shouldn't let it happen at that stage. If the dog approaches the other dog in a mannerly fashion, fine - they'll approach on a curve, sniff butts, play-bow and then play. Even then, it can suddenly turn nasty, if one dog gets scared or over-excited. Ideally, if out of its depth, the dog should return to the owner, and here we have the trust thing again HELP ME I can't do this after all. But if the dog has not learned to trust its owner, and the other dog gets too hyped up.......
It can get like that with small children, too.
It's up to the owners to say "okay, that's enough now" and get their dogs back peacefully. But how many do? Because we get so fixated on this play thing, it is all too easy to ignore the stress signals building. Then we have "he was playing with another dog and it suddenly turned on him/he suddenly turned on it".
So - those are the dogs that react to other dogs because they want to fight or play. Play can easily become fight: fight never becomes play.
Either way, the dog that lunges at other dogs is not in the right frame of mind to meet them.
