\begin{tikzpicture}
  % explode list
  \pie[explode={0, 0, 0, 0.1}] {10/A, 20/B, 30/C, 40/D}

  % explode all
  \pie[pos={8,0}, explode=0.1] {10/A, 20/B, 30/C, 40/D}
\end{tikzpicture}