perl -e 'if($p=fork) {print "unkillable pid:$pn" ;system("ps -l"); sleep(120)}'

unkillable pid:50571
        UID   PID  PPID        F CPU PRI NI       SZ    RSS WCHAN     S             ADDR TTY           TIME CMD
        501 47380 47379     4006   0  31  0  2448416   2900 -      S                   0 ttys000    0:00.36 -bash
        501 50570 47380     4006   0  31  0  2443512   1424 -      S+                  0 ttys000    0:00.01 perl -e if($p=fork) {print "u
#THIS-> 501 50571 50570     2006   0   0  0        0      0 -      Z+                  0 ttys000    0:00.00 (perl)
        501 12795 12794     4006   0  31  0  2448296   1752 -      S+                  0 ttys001    0:00.75 -bash
        501 50123 50122     4006   0  31  0  2448296   2688 -      S+                  0 ttys002    0:00.14 -bash