gistfile1.pl

sub frobnicate {
  my( $self, $data ) = @_;
  ...
  $self->twiddle( $data );
  ...
}

sub twiddle {
  my( $self, $data ) = @_;
  ...
}

# VERSUS

sub frobnicate {
  my $self = shift;
  ...
  $self->twiddle();
  ...
}

sub twiddle {
  my $self = shift;
  my $data = $self->data;
  ...
}