How important is it to indicate if a class implements an interface in Perl?

package Foo::Type::Bar;
sub generate_foo {
    # about 5-100 lines of code
    return stuff here;
}

my $bar_foo = Foo::Type::Bar->generate_foo;
my $baz_foo = Foo::Type::Baz->generate_foo;

package Foo::Type::Bar;
use base 'Foo::Type';
sub generate_foo {
    ...
    return stuff here;
}

$unknown->doodle() if $unknown->can( 'doodle' );

$path_or_OS_I_dont_know_which->format( "c:", 'y' );

if ( $duck->can( 'talk' ) && $duck->can( 'walk' )) {
    $duck->walk();
    $duck->talk();
}

if ( $cand->can( 'walk' ) && $cand->can( 'talk' ) && ... && $cand->can( 'gargle' )) {
    ...
}

$cand->snicker() if $cand->can( 'snicker' );

our @ISA = qw<... Date::Compatible ...>;

sub UNIVERSAL::is_one {
    my ( $self, @args ) = @_;
    foreach my $pkg ( @args ) {
        return 1 if $self->isa( $pkg );
    }
    return 0;
}

sub UNIVERSAL::is_compatible_with {
    my ( $self, $class ) = @_;
    return $self->is_one( $class, "${class}::Compatible" );
}

my $bar_foo = Foo::Type::Bar->generate_foo

my $bar_foo = Foo::Type::Bar::generate_foo

if (Foo::Type::Bar->isa('Foo::Type')) { ... }

my $bar_foo = Foo::Type::Bar::generate_foo;

Foo::Bar->generate
Foo::Baz->generate