See that is the thing. With this it could be anything with variances. Like in nature most combat animals do this same thing in different forms. Snakes do it when they stand high to run off something bigger than themselves and chickens do it to look bigger than their adversary.
But on the same token with bulldogs they are not typical animals. Most times when you see a wagging tail on a dog and there is another dog coming it mean they want to play but not with our dogs. They want to play but with their dead body.
Aye this is a lot of information but great topic of conversation as too many have no idea what they are looking at when it comes to dogs or bulldogs.