Specimen Mechanics

Head Health

When the head health of the specimen reaches 0, its head explodes and takes additional damage. The base damage of the decapitation bonus is given in the below forumla:

/** The last damage amount plus a quarter of the specimen's max hp */
Base Decap Bonus= LastDamageAmount + 0.25 * HealthMax 

It receives all damage modifiers given by perk bonuses, head shot bonus, and weapon resistances/weaknesses and its damage type is the same as the decapitating weapon. Under most circumstances, decapitation will result in an instant death. However, if the bonus damage is not sufficient to kill, a bleed out timer is started and the specimen will aimlessly wander around until the timer reaches 0. The bleed out time varies amongst specimens [1].

Specimen	Bleed Out Time (s)
Crawler, Stalker, Clot, Gorefast, Siren	5
Bloat, Husk, Scrake	6
Fleshpound	7

Stunning

If a specimen is hit with an extremely powerful attack, it will instantly stop moving for several seconds and either bend backwards, or hang its head down. The blow must deal more than 2/3rd of the specimen's base health. In the case of the husk, if the weapon used is an ebr, lar, or crossbow, the damage threshold is lowered to 200 [2]. Any specimen not in the below table cannot be stunned.

Specimen	Stun Threshold
Stalker	67
Clot	87
Gorefast	167
Husk	400 (200)
Scrake	667

Because stunning is based on damage per hit, weapons that deal multiple hits (e.g. shotgun pellets) cannot stun husks and scrakes.

Flinching

If the damage dealt is not enough to reach the stun threshold, it may instead trigger a flinch. While both stunning and flinching can prevent a specimen from attacking, a flinched specimen is still moving. To trigger a flinch, the attack must be from the front and 1) a non-melee attack must deal at least 1/2 of the specimen's base health or 2) a melee attack must deal at least 1/10th of the specimen's base health. In the case that all the conditions are false, the player will instead trigger a mini-flinch [3]. Both a flinch and mini-flinch can interrupt attacks but the mini-flinch effect lasts much shorter.

Unlike the other specimens, scrakes need to be dealt a minimum of 150 damage or hit with a crossbow before either flinch animation is played. Because of the higher damage requirement, melee attacks can only cause normal flinching, and only a few sharpshooter weapons deal enough damage per hit to deal normal or mini flinches. Additionally, scrakes (and fleshpounds) can only flinch once on Suicidal and Hell on Earth, and if a scrake has already been stunned or flinched, he cannot be mini flinched.