Bouts can be one-on-one, or a "mêlée" where more than two fencers are involved. Melees can involve teams of fencers that must work as a group, or an every-man-for-himself "grand mêlée". One important matter of safety in a mêlée is attacking an unaware fencer from behind. Normally this is not permitted unless it is announced before that particular match. When allowed, the attacking fencer must not slash or stab an opponent who doesn't know they are there, but rather must lay their blade on his or her shoulder so the tip is visible to the opponent and verbally tell them they have been "killed" in a loud voice.