You must declare that you are using this feat before you make your attack roll (thus, a failed attack roll ruins the attempt). Stunning Fist forces a foe damaged by your unarmed attack to make a Fortitude saving throw (DC 10 + ½ your character level + your Wis modifier), in addition to dealing damage normally. A defender who fails this saving throw is stunned for 1 round (until just before your next action). A stunned creature drops everything held, can’t take actions, takes a -2 penalty to AC, and loses his Dexterity bonus to AC. You may attempt a stunning attack once per day for every four levels you have attained (but see Special), and no more than once per round. Constructs , oozes , plants , undead , incorporeal creatures , and creatures immune to critical hits cannot be stunned.
The black mamba is diurnal and chiefly an ambush predator, though it has been recorded as hunting partly by pursuit, such as catching pigeons at a watering hole before they can fly high enough to escape. It usually goes hunting from a permanent lair, to which it will regularly return, if the hunting is good and it is not disturbed.  It hunts mainly by sight and in doing so it commonly will raise much of its length well off the ground.  The black mamba does not typically hold onto prey after biting, instead releasing its quarry and waiting for it to succumb to paralysis and die.  This however depends on the type of prey; for example, it typically will hold onto a bird till it stops struggling to escape. If prey tries to escape or defend itself, the black mamba often may follow up its initial bite with a rapid series of strikes to incapacitate and quickly kill its prey.  The snake has been known to prey on hyrax and rock hyrax , bushbabies , and bats.  The black mamba has a potent digestive system and has been observed to digest prey fully within eight to ten hours.