Waving can mean welcome and farewell, whereas scratching your head may indicate that you are at a loss.

挥手表示欢迎和告别，而挠头则表示不知所措。

youdao

I could see you scratching your head.

我能看到你摸不着头脑了。

youdao

All this might have you scratching your head.

所有这一切可能会让你百思不得其解。

youdao

Now their quaint approach to investing might have you standing on the sidelines scratching your head.

FORBES: The Case for a 7700 Dow

If you're scratching your head about the revelation, you're not alone.

ENGADGET

Upon closer inspection, you realize that in addition to federal income tax withholding, the company took out payroll taxes, which leaves you scratching your head.

FORBES: The Top Ten Tax Cases Of 2012, #2: Get Your Refund Claims Ready - The Sixth Circuit Holds That Severance Payments Are Not Subject To FICA