Being in slavery for a decade and witnessing despairing things around him and enduring all the worse things that one could only imagine made Cane well acquainted with such things.
This was one of the reasons why he was very sensitive to the change of attitude as soon as Will approached him after the second monster attack. He could tell right away something horrendous had happened to him, so could he with Iris.
There was something off with the way she acted around Prince Kellan, which made him second guess his opinion about the Prince, despite his impeccable image in front of the people.
"Don't do it when you don't want it, especially when you have an option to choose." This was Cane's way of saying that he wouldn't force her to take the role Prince Kellan suggested.