1. knock
英语解释：to repeatedly hit something, producing a noise
knock一般指用拳头或其他器械猛敲或猛打，也可指用手轻敲某物。
She knocked on the window to attract his attention.
她敲敲窗想引起他的注意。
Theres someone knocking on/at the door.
有人在敲门。
2. tap
英语解释：to hit something gently, and often repeatedly, especially making short, sharp noises
tap多指慢慢地、连续地轻击或轻拍。
She tapped her girl to let her sleep.
她轻轻拍着女儿让她睡觉。
He tapped his forehead knowingly.
他会心地拍拍前额。
3. rap
英语解释：to hit or say something suddenly and forcefully
rap的本意是敲击，急拍，指用手指或木棒等迅速地轻敲或急拍，发出刺耳的声音使大家静下来。
She rapped the table to get everyones attention.
她敲了敲桌子，让大伙注意。
The colonel rapped an order to his men.
上校厉声对他的士兵下命令。
4. pet
英语解释：If you pet an animal, child, etc., you touch it, him, or her gently and kindly1 with your hands.
pet的意思是溺爱，爱抚，多指溺爱或爱抚动物。
Our dog loves to be petted and tickled2 behind the ears.
大家的狗喜欢人在它耳后爱抚、挠痒。
5. pat
英语解释：to touch someone or something gently and usually repeatedly with the handflat
pat的意思是轻拍，轻打，指用手轻拍以示同情、同意或抚摸。所以说，我感觉这个词比较适合描述摸头杀啦。
He patted my head/patted me on the head tenderly.
他温顺地拍了拍我的头。
