system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my dog pick up sticks in her mouth and carry them around?

Doesn't it taste bad?
gpt
When dogs were first domesticated a long, long time ago they were primarily used for hunting for quite some time. After a few millennia of evolution we bred a lot of hunting based instincts into them, one of those being retrieving prey for their master. Basically, when your dog brings a stick to you it's simulating bringing a hunted animal to you. If the dog wants you to throw it, it's mimicking it's natural impulse to chase after prey. If the dog wants to play tug of war with it, it simulates the prey fighting back or something trying to steal it away. (Fun fact, if your dog ever violently shakes it head back and forth it's trying to break the prey's neck) In summary, playing fetch or tug of war mimics the actions we selectively bred dogs to accomplish and gratifies them.