Mutable references in rust and `&mut`

Question

So I am reading through The Rust Programming Language book. Specifically, in this section it says the code

    scores.entry(String::from("Blue")).or_insert(50);

"returns a mutable reference to the value", so my assumption is that I can do this:

    let &mut reff = scores.entry(String::from("Blue")).or_insert(50);
    *reff += 1;

Since &mut is supposed to be a mutable reference. However, when I do that I get this error:

error[E0614]: type `{integer}` cannot be dereferenced
 --> src/main.rs:9:5
  |
9 |     *reff += 1;
  |     ^^^^^

Anyone know why?

Interestingly if I just do:

    let reff = scores.entry(String::from("Blue")).or_insert(50);
    *reff += 1;

It works.