Idiom for knowing someone so well you can tell what they're thinking going to do by small indications

I’m trying to think of an idiom for knowing/ predicting what someone is thinking or about to do because you know them well.

The saying is actually Chinese or Cantonese 你翘一下尾巴我就知道你在想什么了 and roughly translates to "I’ll know what you are thinking if you raise your tail".

To illustrate with a situation, it would be something involving two people. One person reacts to something, say they look up and see rain clouds and then the other person knows that the first person will want to go back to get an umbrella. Because they saw them look at the cloud and know their thinking, they were able to guess what they would do.

Another example, someone is eating salad and makes and looks around the table, then the other person hands them the salt. Because they know them so well they knew what they were thinking.