Q:

Popup bubble in beamer presentation

I'm working on beamer slides for an introduction presentation. As the purpose is more of a fun, my colleagues had the idea of letting some logos (e.g. TeX lion) popup for a second or two and then disappear automatically.
I know that, I could do this with overlay effects and click two times to let the popup bubble appear and disappear. But I think it would be better, if the bubble would disappear after a second or two automatically without any user interaction.
Is there any possibility to achieve something like this?

A:

You need to view the resulting PDF in full screen mode of Adobe Reader. See Beamer Guide §14.3 Slide Transitions for more information.
\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{shapes.callouts}
\begin{document}
\begin{frame}
    \frametitle{There Is No Largest Prime Number}
    \framesubtitle{The proof uses \textit{reductio ad absurdum}.}
    \begin{theorem}
        There is no largest prime number.
    \end{theorem}
    \begin{proof}
        \begin{enumerate}
        \item Suppose $p$ were the largest prime number.
        \item Let $q$ be the product of the first $p$ numbers.
        \item Then $q+1$ is not divisible by any of them.
        \item But $q + 1$ is greater than $1$, thus divisible by some prime
            number not in the first $p$ numbers. \qedhere
        \end{enumerate}
    \end{proof}
    \uncover<2>{\tikz[remember picture,overlay]{
        \node[inner sep=10pt,cloud callout,shading=ball,]at(8,4)[white]{
            Powered by \LaTeX};}}%
    \transduration<1>{2}%
    \transfade<2>%
    \transduration<2>{2}%
    \transfade<3>%
\end{frame}
\end{document}

The following screenshot shows that the PDF contains 3 pages/slides but all numbered "1". In full screen mode, The following happens in sequence:

the 1st slide is shown for 2 seconds. (since I said \transduration<1>{2}) 
and then the 1st slide is fading out while the 2nd slide is fading in. (since I said \transfade<2>).
the 2nd slide is shown for 2 seconds. (since I said \transduration<2>{2}) 
the 2nd slide is fading out while the 3rd slide is fading in. (since I said \transfade<3>).
the 3rd slide is shown forever. (I said nothing)

