Using HTML markup to make captcha recognizing bots work harder

I am sure there are thousands ways to make text captcha harder for bots. One idea I just figured out is when we mix words from the question with some crap words so the question looks like What _bla bla bla_ is _do-da-du_ seven _hey there_ hundred _brum-brum_ and _go-for-it_ forty _do this_ four _again_ as _blah_ a _mlah_ number? I marked crap words with underscores here. Then we can easily style these words with CSS to be faded or grayed out or anything like that so that user could clearly see the question, and trash words wouldn't be visible clear enough. It could make bots work harder. More than that, we can use inner HTML markup to make the question look like crap when we look into source still looking good if we look at it in browser. What do you think?