Make a mental note:
To make an effort to remember something.
“Make a mental note” 的意思是 “试着记住一件事情”。如果想说明要记在脑子里的事情具体是什么，可以说 “make a mental note of something”。
例句
I don’t have a pen and paper at the moment, so I’ll make a mental note of it.
我现在没有纸和笔，所以我会记在心里。
I’ll make a mental note of the date of the wedding.
我会在脑子里记下婚礼的日期。
You’ll need to make a mental note of what she says in the meeting.
你需要在心里记下她在会议上说的话。
