Since this is an AoA, $res->[0]->[0] will also work consider

perl -e"$a=[['ref']];print q|$a\n$a->[0]\n$a->[0]->[0]\n$$a[0]\n$a->[0
+][0]\n$a->[0]->[0]|; "


__END__
ARRAY(0x183f0d4)
ARRAY(0x183efd8)
ref
ARRAY(0x183efd8)
ref
ref
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