From the NannyMUD documentation

LAST CHANGE

2002-12-15

FUNCTION

NAME
        changed_gender_hook - Hook gender changes


LOCATION
        /obj/living_functions

AVAILABILITY
        Any object can register this hook.

DESCRIPTION
        'changed_gender_hook' is called after the gender has been
        changed in a living object.

        ARGUMENTS
        
        changed_gender_hook(
             ({ New gender, // This is an integer.
                Old gender  // This is an integer
		}),
	     player_object
        )