system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why do we sometimes talk while asleep?
gpt
Long story short, it's a bit like a mild form of sleepwalking - i.e., the failure of the neurochemical measures your brain undertakes to ensure that your body does not actually react to anything you experience while dreaming. So while there normally would be inhibitors which would prevent your sleeping body from doing stuff it should only do while it is awake, these inhibitors sometimes don't work.

Why exactly this happens still isn't entirely understood by science. Potential factors may include 

* excessive stress (i.e., your brain being on such high alert that it can't shut down entirely even when it should)
* fever (i.e, disturbance of your general brain chemistry due to disease)
* genetics (i.e., people are more likely to sleepwalk when their parents also have a history of sleepwalking, as they inherit the responsible traits of the brain)

Bear in mind this is a very simplified answer, as human neuroscience in general is an extremely complex topic.