How do I show a bootstrap tooltip with an SVG object?

I'm going crazy trying to understand why I can show tooltips on regular HTML elements, but not on D3-generated SVGs: http://jsfiddle.net/nachocab/eQmYX/5/

What am I doing wrong?

$(document).ready(function () {
    $("a").tooltip({
      'placement': 'bottom'
    }); // this works

    $("my_circle").tooltip({
      'placement': 'bottom'
    }); // this does not work
});