Other scientists believe, however, that yawning is a form of communication. This theory attempts to explain why yawning seems to spread from person to person. This kind of behavior is called "contagious yawning" and carries with it a possible social message. Scientists are not yet sure what exactly the message is, but they believe people who have more social empathy are more likely to start yawning when they see someone else yawning. Scientists will continue to investigate the mystery of the yawn. Is it a leftover behavior from before humans had language? Was it a "Hey, I'm sleepy. Let's go to sleep" message? Or is it really just a way to keep our brains cool? While this behavior still is largely a mystery, one thing is certain: you are probably fighting the urge to yawn right about now. Which line shows the main idea of the bolded paragraph? Yawning is a form of communication Yawning seems to spread from person to person Scientists are not yet sure what exactly the message is People who have more social empathy are more likely to start yawning