Act 3, Scene 4

Othello story about the handkerchief is interesting and open for interpretation. It may just be something he's made up, simply to garner a reaction. On the other hand, his mother may have given it to him, and he might just believe it is magical.... which would explain his reasons for giving it to Desdemona..... to insure her fidelity. Othello has made the handkerchief the proof of Desdemona's cheating. Either way, he uses the handkerchief to gauge her guilt, and in his eyes, she fails.