Pop-Up Plugin

I am looking for a plugin that would allow me to embed an informational pop up in the body of a post or page. It would work something like this:

Here is some text about a [popup text='here is more text on that subject']certain subject[/popup].

I would want it to show something like:

Here is some text on a certain subject.

When the reader clicks or mouses over “certain subject” a small pop up would show “here is more text on that subject’.

Ideally, I would want it to be a simple plugin that doesn’t do a host of other things. I definitely don’t want to have to write out the popup content in another window and then link to it. I want to write it right there as I’m composing my post or page.