$henry->attack($joe);
    $joe->attack($henry);

sub attack {
  my ($self,$target) = @_;
  ... # compare dex/abilities to see if you hit the target
  if ( $hit ) {
    ...  # compute damage from the attack
    $target->damage( $amount, $self );
    ... # emit messages about the attack
  } else {
    ... # emit messages about a miss
  }
}
sub damage {
  my ($self, $amount, $attacker) = @_;
  ... # adjust amount for armour, etc.
  $self->{_hp} -= $amount; # this assumes the object is a hashref
      # this may not be the case ... see 'perldoc perltoot'
  if ( $self->{_hp} <= 0 ) {
    ... # whatever to do for death
  }
}