Tagging an equation with a tikz duck

Question

I would like to label and equation with a tikz duck from the tikzducks package and refer back to it later, like so:

The obvious solution:

\usepackage{tikz}
\usepackage{tikzducks}
\usepackage{amsmath}

\section*{Question 1}
\begin{enumerate}[(a)]
\item

\[a^{2} + b^{2} = c^{2} \tag{$\begin{tikzpicture}[scale=0.2]
    \duck
    \end{tikzpicture}$} \label{C}\]

From equation \(\eqref{C}\), $b^{2} = c^{2} - a^{2}$.

\end{enumerate}

gives me the error: TeX capacity exceeded, sorry [input stack size=5000]. However when I put the duck elsewhere in the image, I do not get this error, the document compiles and I get to see my duck (quack)!

(I might add that it doesn't matter whether or not the tikzpicture environment is placed inside math mode or not.)

I can't seem to find a way to stop this error from happening.

Thanks for looking at my question.

Answer 1

\documentclass{article}
\usepackage{tikz}
\usepackage{tikzducks}
\usepackage{amsmath}
\usepackage{xparse}
\usepackage{enumerate}
\NewDocumentCommand\ducktag{}
{%
  \begin{tikzpicture}[scale=0.2]
    \duck
  \end{tikzpicture}%
}
\begin{document}
\section*{Question 1}
\begin{enumerate}[(a)]
\item 

\[a^{2} + b^{2} = c^{2} \tag{\ducktag} \label{C} \]

From equation \eqref{C}, $b^{2} = c^{2} - a^{2}$.

\end{enumerate}

\end{document}

You could also add an argument for options:

\documentclass{article}
\usepackage{tikz}
\usepackage{tikzducks}
\usepackage{amsmath}
\usepackage{xparse}
\usepackage{enumerate}
\NewDocumentCommand\ducktag{m}
{%
  \begin{tikzpicture}[scale=0.2]
    \duck[#1]
  \end{tikzpicture}%
}
\begin{document}
\section*{Question 1}
\begin{enumerate}[(a)]
\item

\[a^{2} + b^{2} = c^{2} \tag{\ducktag{}} \label{B} \]

From equation \eqref{C}, $b^{2} = c^{2} - a^{2}$.

\item 

\[a^{2} + b^{2} = c^{2} \tag{\ducktag{body=blue}} \label{C} \]

From equation \eqref{C}, $b^{2} = c^{2} - a^{2}$.

\item 

\[a^{2} + b^{2} = c^{2} \tag{\ducktag{body=red}} \label{D} \]

From equation \eqref{B}, \eqref{C} and \eqref{D} $b^{2} = c^{2} - a^{2}$.
\end{enumerate}

\end{document}