"Pound" or "pat" on the head is an expression that is often used to describe a physical action where someone gently hits or taps the top of someone else's head with their hand, usually as a form of affection or playfulness.

The origin of this expression is unclear, but it is a common gesture that is seen in many cultures around the world. It is often used as a way to show affection or playfulness, especially between friends or family members.

Here are some examples of how "pound" or "pat" on the head can be used in a sentence:

"She playfully pounded her pttle brother on the head as he laughed and tried to wriggle free." (她拍打她弟弟的头，他笑着试图挣脱。)
"He patted his dog on the head as a reward for performing a trick." (他拍了拍他的狗的头，作为它表演节目的奖励。)
"The father gently pounded his son's head as a sign of affection." (父亲轻轻地拍打他儿子的头，表示亲昵。)