use Data::Dumper;

my @matrix = ();
$matrix[2]->[3]= "What's goin on?";

print "Before grep:\n", Dumper(\@matrix);

grep{ /Huh?/ }@$_ for @matrix;

print "\nAfter grep:\n", Dumper(\@matrix);

__DATA__
Before grep:
$VAR1 = [
          undef,
          ${\$VAR1->[0]},
          [
            ${\$VAR1->[0]},
            ${\$VAR1->[0]},
            ${\$VAR1->[0]},
            'What\'s goin on?'
          ]
        ];

After grep:
$VAR1 = [
          [],
          [],
          [
            undef,
            ${\$VAR1->[2][0]},
            ${\$VAR1->[2][0]},
            'What\'s goin on?'
          ]
        ];