sub analysis {
    ....
    returns one of 'critical', 'harmless', 'unseen';
}
sub parse_body {
    my $self = shift;
    $self->set_severity(analysis($self->mailbody))->severity;
}
sub set_severity {
    $_[0]{severity} = $_[1];   # Substitute your favourite OO implementation
    $_[0];
}
sub severity {
    $_[0]{severity};
}