Ok, when you put anything if your 2nd hand, and you have the Chorus plant. if you toss the item in your 2nd hand and right click the chorus plant, you get same item again.
1. Put anything (Im going to say diamond) in your 2nd arm
2. Drop that said item on the floor
3. put the chorus plant in your main arm and right click it.
4. Enjoy your duplicated diamonds.

https://www.youtube.com/watch?v=RBLoNukK4rQ&feature=youtu.be

Video to see better proof.