sub add_content {
	my $self = shift;
	my $content = shift;
	$words = [ split(/\s+/, $content) ];
        for ($i=0; $i < scalar(@$words) ; $i++) {
                my $first_word = lc($words->[$i]);
                my $second_word = lc($words->[$i+1]);

                # 2 word phrases
                if ($self->is_relevant_word($first_word , $second_word) && $first_word ne "$second_word") {
                        my $phrase = $first_word . " " . $second_word;
                        $self->{_related}{$phrase}++;
                        $self->_rate_phrase($phrase);
                }
	}
}