\font\donteveruseoutsidecartoons="Comic Sans MS" at 14pt
\font\donteveruseoutsidecartoonstwo="Comic Sans MS/IB:slant=.3pt" at 22pt
\input tikz
\usetikzlibrary{shapes.callouts,positioning}
\tikzpicture[mycallout/.style={draw,ellipse callout,inner sep=1.2ex,
    callout relative pointer={#1}}]
  \node[mycallout={(.5cm,-.5cm)}] (ico) {\donteveruseoutsidecartoons Be rational};
  \node[mycallout={(-.5cm,-.5cm)}, right=of ico] (pco) {\donteveruseoutsidecartoons Get real};
  \node[below=.1ex of ico.pointer] {\donteveruseoutsidecartoonstwo i};
  \node[below left=.1ex of pco.pointer] {\donteveruseoutsidecartoonstwo π\vphantom(};
\endtikzpicture
\bye

<tex> d = \frac{m_0^3}{\sqrt{3-\frac{v^2}{c^2}}} + \sqrt[3]{a^2 + b^2} - \log_3 \cos \frac{\pi}{3} </tex>