I saw the answers of this other question about the scene in The Avengers where Loki tries to do his mind control on Tony Stark, so I started to wonder that why Loki didn't realize that he just has to move his staff to another body part of Tony.
I mean is Tony having an arc reactor a big secret? Because Loki seems to have much knowledge about the Avengers and earth. Loki is not as hot-headed as his brother, he must realize this at least.