pick up on it

Reader's Digest 11月号の記事 'Life Lessons From Boot Camp' から引用します。
Never argue with drill sergeants.
If you have a differing opinion, ask whether you can give yours. They'll tell you whether there's any room for discussion. If not, salute and move out smartly. Don't roll your eyes or let your attitude show, either. The drill sergeants will pick up on it and eat your lunch.
慣用句と思われる "pick up on" の意味を調べます。
・Oxford English Dictionary: Become aware of or sensitive to something.: 'she is very quick to pick up emotional atmospheres’
・McGraw-Hill Dictionary of American Idioms and Phrasal Verbs: to become alert to something; to take notice of something; to learn or catch on to something. She's real sharp. She picks up on everything. The cop picked up on the car with the expired license plates.
"pick up on" は日本語の空気を読むの表現に使えそうです。