Lend me your brains

The 'reverse' gearing takes effect as soon as you apply back-pressure on the pedals, or the rotation if the pedals (caused by the reverse gearing) catches up to your pedalling motion.
You would not need to start skidding, and could stop smoothly by resisting the rotation of the pedals.
More thought experiments! ;-)

[Groan] It makes my head hurt.

I'm off to misc & meaningless - it's more my speed.