Also wrong on the open differential, MJ. (This isn't your day.)
When one is stuck, the other spins in the proper direction. But, with the car on a lift and the transmission in gear, if you turn one forward, the other goes backward.
I had a buddy weld up the spider gears on a '56 Chevy many years ago. While driving it on the street, I could hear the tires chirp as I turned a corner at slow speed and while I parallel parked, but, other than that, I couldn't notice the difference. The right rear no longer went up in smoke at the strip, though.