\documentclass[pstricks]{standalone}
\usepackage{pst-contourplot,multido}
\begin{document}
\multido{\r=-2+0.08}{50}{
\begin{pspicture}(-6.4,-4)(6.4,4)
\psframe*(-6.4,-4)(6.4,4)
\pstVerb{/xC \r\space def
         /FonctionMetaballs {
          1 x xC sub dup mul y dup mul add sqrt div
          0.5 x xC add dup mul y dup mul add sqrt div
          add
          1 sub
         } def}%
\psContourPlot[unit=2,a=0.1,linewidth=0.025,linecolor=red,fillcolor=cyan,Fill,ReverseColors,function=FonctionMetaballs](-4,-2)(4,2)
\psdots(! xC 2 mul 0)(! xC neg 2 mul 0)
\end{pspicture}}
\end{document} 