garble function contest

Remember that away message on aim that said how:

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Anyway I'm trying to make a function that would do that to an entire page. There are a few rules for this function.

1. less then 4 characters leave alone.
2. non-alphanumeric characters don't count as part of the word.
3. hyphenated words are really two words
4. words must get garbled if length >= 4 (can't be like the original)
5. The first and last chars stay the same and only the middle chars get garbled (Thanks Hersheezy)
6. the text should always be random and produce unique garbling on each run
7. Pure javascript and iterates on all text nodes
8. Shortest sweetest code wins.

Anyway it seems simple enough to implement, how's about starting a contest to see who could make the cleanest clearest code to accomplish this task. Feel free to borrow without recognition from my code (I def have)

If i missed anything add it in the comments. Anyway I worked on it very hackishly and here's me showing my less than par work

DEMO

var i, j, words, textNodes, punct = /[^a-zA-Z0-9]/;

Array.prototype.shuffle = function() {
    for (var i = 0; i < this.length; i++) {
        var j = i;
        while (j == i) {
            j = Math.floor(Math.random() * this.length);
        }
        var tmp = this[i];
        this[i] = this[j];
        this[j] = tmp;
    }
    return this;
};

String.prototype.shuffle = function() {
    return this.split('').shuffle().join('');
};

function transverse(element, array) {
    if (!array) array = [];
    if (element.nodeType === 3) {
        array.push(element);
    } else {
        for (var i = 0; i < element.childNodes.length; i++) {
            transverse(element.childNodes[i], array);
        }
    }
    return array;
}

function garble(str) {
    if (!str) return '';
    str = str.trim();
    if (/-/.test(str)) {
        str = str.split('-');
        for (var i = 0; i < str.length; i++) {
            str[i] = garble(str[i]);
        }
        return str.join('-')
    }
    if (punct.test(str.charAt(0))) {
        return str.charAt(0) + garble(str.slice(1));
    }
    if (punct.test(str.charAt(str.length - 1))) {
        return garble(str.slice(0, -1)) + str.charAt(str.length - 1);
    }
    if (str.length < 4) return str;
    if (str.length === 4) return str.charAt(0) + str.charAt(2) + str.charAt(1) + str.charAt(3)
    return str.charAt(0) + str.substr(1, str.length - 2).shuffle() +
        str.charAt(str.length - 1);
}


window.onload = function() {
    textNodes = transverse(document.documentElement);
    for (i = 0; i < textNodes.length; i++) {
        words = textNodes[i].data.split(' ');
        for (j = 0; j < words.length; j++) {
            words[j] = garble(words[j]);
        }
        textNodes[i].data = words.join(' ');
    }
};