$\ = "\n";

{
   my %hoa = ( head => [ 'abc', 'def' ] );
   print shift(@{$hoa{head}});   # abc
   print @{$hoa{head}};          # def    -> ok
}

{
   my %hoa = ( head => [ 'abc', 'def' ] );
   my $data = $hoa{head};
   print shift(@$data);          # abc
   print @{$hoa{head}};          # def    -> ok
}

{
   my %hoa = ( head => [ 'abc', 'def' ] );
   my @data = @{$hoa{head}};
   print shift(@data);           # abc
   print @{$hoa{head}};          # abcdef -> BAD!
}