猜不透

cāi bu tòu mǒu rén xīn si

猜不透某人心思

have not read somebody's thoughts

wǒ cāi bu tòu tā de xīn shì

我猜不透她的心事。

I can't figure out what's on her mind.

zhè zhǒng shū ràng nǐ bù kàn dào zuì hòu dōu cāi bu tòu

这种书让你不看到最后都猜不透。

It's the kind of book that keeps you guessing right to the end.