don't talk nonsense at blah.pl line 23.
  21 learn('nothing');
  22 sub blah (\[&]) {
  23     warn "don't talk nonsense";
> 24     $_[0]->();
  25 } 
  26 sub learn {
  27     my $self->teach(shift);
Can't use string ("bar") as a subroutine ref while "strict refs" in use at blah.pl line 24.