1. Have a second item that is able to be picked up into your hands. (Cannot be a item already in your inventory)
2. Go up to a ladder and drop the object near the ladder. (You know you dropped it in the correct place if you can see the item in your "Nearby" section of your inventory while on the ladder)
3. Then while on the ladder, open your inventory and see if you can pickup the object into your hands. If you can, then obviously put the item into your hands.
4. If done correctly you should see the object in your hands while on the ladder, now proceed to get down and off the ladder.
5. Viola! You now have done the Object Arm Glitch