How to open a temporary comics-like balloon in a beamer slide?

I would like to open a temporary comics-like balloons to explain a specific word in a beamer slide. Somebody has suggestions?

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Following up on Ulrich's suggestion, here's some example code that will do it. I'm sure that there are more elegant solutions, and I'm probably including some options that aren't necessary, but it will hopefully give you the idea.

\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{shapes.callouts}

\begin{document}
\begin{frame}
\frametitle{An Unexpected Website}

We learnt of this trick from tex.SX\tikz[remember picture] \node (a) {\vphantom{X}};

\begin{tikzpicture}[remember picture,overlay]
\path<2> (a.east) ++(0,1) node[anchor=west,ellipse callout,fill=red!50,opacity=.5, callout absolute pointer={(a.mid)}]  {tex.stackexchange.com};
\end{tikzpicture}

\pause
\pause

And now for something completely different.
\end{frame}
\end{document}


With result:

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Great! Thank you both! bye gabriele –  gabriele vezzosi Nov 15 '10 at 20:39
For the record, Ulrich Schwarz posted an answer to this which pointed out where to find the details. I merely converted that to a working example. That explains my first comment. Ulrich has now deleted that answer, but I certainly didn't intend to gazump it! –  Loop Space Nov 15 '10 at 21:35