$ perl -E'
   sub show { say &Internals::SvREFCNT( \undef ); }
   show(); push @a, \undef for 1..5; show();
'
2147483623
2147483628

##</code><code>##

$ perl -E'
   sub show { say &Internals::SvREFCNT( \undef ); }
   show(); { my @a; $#a = 5; } show();
'
2147483623
2147483617