There are three 1 under research: two 2 and one psychological.

The first suggests that yawning is triggered by a 3 : an initial yawn, and it is called 4 pattern. It is similar to a 5 effect.

The second is known as the 6 effect. It states that people imitate each other’s behaviour without knowing it. This behaviour might be possible due to 7 which are also important for learning.

The third one is called the  8 . Scientists set up an experiment to prove that 9 would yawn at the sound of yawning and they also discovered that we yawn more frequently at the yawns of 10 rather than strangers.