\node (rec) [right=of s2.north,yshift=-3em,fill=gray!15,label={[xshift=1em,label distance=-5pt]above:{\tiny interpreter}}] {\verb#blink (Not x)#};
\draw (s1.south) -- (d1.north);
\draw (s1.south) -- (s2.north);
\draw (s2.south) -- (wd.north);
\draw (s2.south) -- ([xshift=-1.5em]rec.north);
\node (rec) [right=of s2.north,yshift=-3em,fill=gray!15,label={[xshift=1em,label distance=-5pt]above:{\tiny interpreter}}] {\verb#blink (Not x)#};
\draw (s1.south) -- (d1.north);
\draw (s1.south) -- (s2.north);
\draw (s2.south) -- (wd.north);
\draw (s2.south) -- ([xshift=-1.5em]rec.north);