Use of uninitialised value... but it is defined ?!

[seki]

Hi Monks, I got the "Use of uninitialised value" warning but the variable looks like being defined to me, so it must be a perlism that I am missing...
Maybe It is related to the closure mechanism, but in that case I do not get the point...

>perl -w test_mod.pl
Use of uninitialized value $variable in concatenation (.) or string at test_mod.pl line 12.
Use of uninitialized value $variable in say at test_mod.pl line 15. Foo::begin

test_mod.pl

use strict;
use warnings;
use feature 'say';

Foo->test();

{
    package Foo;
    
    my $variable = "bar";
    
    BEGIN { say __PACKAGE__."::begin $variable"; }
    
    sub test {
        say $variable;
    }
}