Piano players who do drills when they are children to improve dexterity in their left hands experience as a result.

I believe the answer is: brain changes that greatly improve dexterity

As we are conditioning ourselves to do something with a certain part of our body, our brain would eventually improve and adjust itself to make us able to do that thing better, even on automatic function. The same thing happen to soccer youths who are continuously trained to use both of their leg to make a maneuver ever since they're little.

the 5th amendment is about the justice system

explanation:

there is no double jeopardy

due process

grand jury

and that you can’t incriminate yourself