"Smashers" are able to use the raptorial appendage with such a force, particularly the gonodactylids, that they are able to smash the glass of double walled aquariums in the laboratory. These smashers are able to use this immense force to kill same-species competitors with one blow. Caldwell et al. describe how two stomatopods generally display severe fighting behaviour when they have an encounter, both between species and within the same species, and males and females display the same level of this behaviour except in breeding season. Most species of stomatopods, regardless of the type of appendage, ordinarily deliver blows during agonistic encounters with the dactyl closed. When the dactyl is open, the result is usually serious injury or death of the opponent. These crustaceans may deliver blows with the dactyl open but generally only in situations of extremely intense fighting displays, which are rare amongst most species.