Complex sentence: Tickling is a form of physical intimacy which also serves as a bonding mechanism between friends, and is classified by psychologists as part of the fifth and highest grade of social play which involves special intimacy or "cognitive interaction".
Split into simpler sentences: Tickling is a form of physical intimacy which also serves as a bonding mechanism between friends. It is classified by psychologists as part of the fifth and highest grade of social play which involves special intimacy or "cognitive interaction".