Sentence:  “I'm warning you. I'm going to get angry. D'you see? You're not wanted. Understand? We are going to have fun on this island. Understand? We are going to have fun on this island! So don't <WSD>try it on</WSD>, my poor misguided boy, or else—” 
Meaning of the word marked with <WSD> tags:  To test someone to see how much bad behaviour they will tolerate; to try to deceive someone to see how gullible they are.