Agreed again about understanding the difference between call by reference or call by value :) The point I tried to make was that in an dynamic language you should be careful about the assumption that the method input is indeed a primitive type.
Not really an issue in code like this Kata of course. Unless somebody built a class that overloads & and >> :D

Agreed that it doesn't affect the outer scope's value.
However, I would argue that in a dynamically typed language, one should be extra careful about this.

This one modifies the input variable. Isn't that considered bad practice?