Because most observe Hao occurred a thot That is, if a particular person, other people who see Hao to Hao as similar to a behavior that is able to convey to each other.
Because by observing the yawning often occur together in a cascade. That is, if a person yawn. Then others saw it as a yawn. Similar behavior can be conveyed with each other.
Because of the observation oscitancy most often occur with each other around. That is, if there is any one person yawn. Then another person I was finding Stewart three. Similar to a behavior that can be transmitted to each other.