\usepackage {pstricks}
\begin{pspicture}(-.2,-.5)(3,2)\showgrid
\rput(.5,.5){\rnode{A}{\psframebox{Cat}}}
\rput(2.5,1.5){\rnode{B}{\psframebox{Dog}}}
\ncloop[loopsize=.25,angleB=180]{A}{B}
\end{pspicture}
