When someone gets nervous, their brain sends out a message to speak, but it gets confused. Like when you're trying to say your name and suddenly forget what it is. It's like a traffic jam in the brain that makes speech stop and start quickly.
What Causes This?
Sometimes, being nervous can make our brains send signals too fast or not quite right. That causes the person to repeat sounds or get stuck on certain words, just like when you're trying to say something really important but your brain is busy thinking about everything else.