As others have pointed out, you're assigning the contents of @_ to the hash. @_ happens to contain just a hash reference. Now what can you do about this? In all but pathological cases, you won't be using hash-references as hash-keys, so you can do the following: (beautification left as an excercise to the reader)

sub describe {
    my %person;
    if (@_ and ref($_[0]) eq 'HASH') {
        %person = %{+shift};
    }
    %person = @_;
    ...
}
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This "flattens" the first argument of the sub if it is a hash reference. Thus, if you call describe( { some=>'args' }, more => 'of_them' ), you'll get %person=(some=>'args',more=>'of_them'); Please note that the ordinary arguments overwrite those of the flattened hash in case of matching keys.