I said:

> arranging a file so that it is syntactically correct in two
> different languages at the same time is a common trick...
> Larry Wall was a repeat winner in the IOCCC.

Another related item I forgot about: perlrun says:

           #!/bin/sh -- # -*- perl -*- -p
           eval 'exec perl -wS $0 ${1+"$@"}'
               if $running_under_some_shell;
[download]

If this code is run by /bin/sh, it tells the shell to execute perl instead to run the script. But when perl sees this code, it does nothing.