package Foo;

my $_private = sub { ... };
my _private = sub { ... };

sub foo {
    my $self = shift;
    
    # we can specify the full package name
    $self->Foo::_private();
    
    # we can call as a subroutine
    _private($self);
    
    # we can use lexically scoped subs
    $self->$_private();
};