How is “spy on” used?

In Tucker and Dale vs. Evil (2010), one line is: “- Wait, you...you were spying on us? - No. No, what? No!”

Which movie is “spy on” from?

The clip at the top of this page is from Tucker and Dale vs. Evil (2010).

- Wait, you...you were spying on us? - No. No, what? No!

8 作品で登場 · 1 本目

to watch sb / sth secretly

27 本の映画に登場

定義：Oxford Advanced Learner's Dictionary 第 9 版