Chapter 3 , claryifying that a mutable variable can be shadowed.

[low-perry]

On chapter 3 , shadowing section the text goes to great lengths to explain the difference between mutability and shadowing, somewhat implying that you can have either/or (not stated anywhere).
I think it would be a good idea to add a note clarifying that you can also shadow a mutable variable and maybe encourage the reader to try it for themselves.

NOTE: It is possible to shadow a mutable variable.