Did you know dogs can tell another dogs emotion by the direction they wag their tail?
In lab experiments when dogs saw an image of a dog wagging its tail to left, they got anxious. When the dog saw an image of a dog wagging its tail to the right they were relaxed. This isn't the first scientists knew this.
In Italy, when a dog saw something like their owners, they wagged their tails to the right. When they saw something like an unfamiliar dog, they wagged their tails to the left.
Another test, dogs had to watch a video of a dog silhouette while wearing a thing on them to measure their heart rate. Same with everything. When they saw a dog wagging its tail to the right they stayed relaxed. When they saw a dog wag its tail to the left, their heats started beating faster and they looked anxious.
I think that it's very cool how they can figure out the different reactions of dogs just by the wag of their tail.