Beamer add explanation to items

Question

I have a list in Beamer. The list is a bunch of observation. Some of the observations are not obvious. So I want to add some notes for some of the item.

Using \onslide wouldn't work because it retains space in the slides it's not visible. And \only is causing distracting jumps.

It'd be best if I could add some speech bubbles, but that seems overly complicated. I will settle for a generic way add a non-jerky note to list items.

 

This is what I have now. (I removed some irrelevant part of the code for easier understanding. So first itemize list in the gif is not in the code.)

\documentclass{beamer}
\usepackage{animate}
\usepackage{verbatim}
\usepackage{amsmath}
\usepackage{hyperref}
\begin{document}
\metroset{block=fill}
\begin{frame}[t, label=comp-notes]
    \frametitle{Feedback Vertex Set in Tournaments Compression}
We prepare for Comp-FVST:

\onslide<2-> {Notice that ---}

\begin{itemize}

    \item<2-> $V_k$ is a directed feedback vertex set of size $k$ of $T_k$.

        \only<3>{
            {\small Because if you remove all vertices you remove all
            cycles as well.}
        }

    \item<5-> If $X$ is a directed feedback vertex set of $T_i$, then $X \ \cup
        \ \{v_{i+1}\}$ is a directed feedback vertex set of $T_{i+1}$.

\end{itemize}


\end{frame}

Answer 1

Inspired by this idea: You can use TikZ and create callout annotations like this:

\documentclass{beamer}
\usepackage{animate}
\usepackage{verbatim}
\usepackage{amsmath}
\usepackage{hyperref}
\usetheme{metropolis}
\usepackage{tikz}
\usetikzlibrary{tikzmark,shapes.callouts}
\newcounter{annotation}
\newcommand<>{\annotate}[2]{%
    \alt#3{%
        \stepcounter{annotation}%
        \tikzmarknode{ann\theannotation}{#1}%
        \tikz[remember picture, overlay]{
            \node[anchor=pointer, ellipse callout, callout relative pointer={(-.5,-.5)}, fill=yellow!75, font=\small, text width=5cm, align=center] at (ann\theannotation.north) {#2};
        }%
    }%
    {#1}%
}
\begin{document}
\metroset{block=fill}
\begin{frame}[t, label=comp-notes]
    \frametitle{Feedback Vertex Set in Tournaments Compression}
We prepare for Comp-FVST:

\onslide&lt;2-&gt; {Notice that ---}

\begin{itemize}

    \item&lt;2-&gt; $V_k$ is a directed feedback \annotate&lt;3&gt;{vertex set}{Because if you remove all vertices you remove all cycles as well.} of size $k$ of $T_k$.

    \item&lt;4-&gt; If $X$ is a directed feedback vertex set of $T_i$, then $X \ \cup
        \ \{v_{i+1}\}$ is a directed feedback vertex set of $T_{i+1}$.

\end{itemize}


\end{frame}
\end{document}

How to use: Place the word or words to which you wish to point the speech mark to in the first argument and place the annotiation that should be inside the bubble in the second argument. Also, you can use the standard overlay specification the beamer class provides.