scramble string, but still readable

main.rs

use rand::seq::SliceRandom;

/// If you mix up the order of letters in a word, many people can slitl raed and urenadnstd tehm. Write a function that
/// takes an input sentence, and mixes up the insides of words (anything longer than 3 letters).
///
/// Example:
///
/// ```
/// > scramble(["A quick brown fox jumped over the lazy dog."])
/// > "A qciuk bwron fox jmepud oevr the lzay dog."
/// ```

fn main() {
    let mut sentence = "A quick brown fox jumped over the lazy dog.".to_string();
    scramble(&mut sentence);
    println!("{}", sentence);
}

fn scramble(sentence: &mut String) {
    let mut i = 0;
    while i < sentence.len() {
        if let Some(word_len) = sentence.get(i..).unwrap().find(' ') {
            if word_len >= 4 {
                let inner = sentence.get_mut(i + 1..i + word_len - 1).unwrap();

                // shuffle it
                let mut rng = rand::thread_rng();
                unsafe {
                    inner.as_bytes_mut().shuffle(&mut rng);
                }
            }

            i = i + word_len + 1;
        } else {
            break;
        }
    }
}