Hello, I played my first session with my group last weekend and as they were fighting off zombies one of the players wanted to go for a head shot with his kukri i was wondering if i should add more negative dice to that because of the called shot or not? Also another player was running over zombies with a truck he stole how do I accumulate the damage to the truck because of all the zombies the player ran over? If anyone can answer those questions i'd appreciate it!

Normally if you're going to take a headshot at something it requires you to be relatively still and focused aiming for the head. In this situation I'd add one positive dice for focusing and taiking aim but maybe add a negative or two as well, one for having to take aim in the middle of a zombie filled location and one for trying to hit a moving target bearing down on you.

Also if your PCs are unfamiliar with weapons or firearms perhaps add an additional negative dice. I know I'd personally find it hard to take aim at a zombies head in the middle of the apocalypse with zero weapons training so the negative dice just need to reflect this.

As for vehicle damage I'm not sure, I'd probably have the driver perform some kind of test upon colliding with a pack of zombies and then on a fail result have something happen that causes damage to the vehicle (smashed widscreen, blown tyre etc)

Thanks that cleared things up a lot. but the funny thing is they are not using guns, they are using swords!! so ill just use what you said about not being trained with the weapons rather than the guns, and add negative dice for being surrounded, or the weapons to heavy or to short to reach them.

Negative dice do not directly/wholly represent the difficulty of an action. They really represent the risk primarily, the diff (failure inherent to that risk) is incorporated into that. Number of successes is the direct representation of absolute difficulty.

Accordingly, with a normal "luck" headshot being paired successes, I would put a called-shot maybe at three unpaired successes, but if you don't achieve that success threshold you miss completely. Achieving the three is of course insta-kill.

I wouldn't add any positive die to the attack beyond the normal sums of 1+traits+equipment+environment+assistance. However I would add 1 or maybe even 2 additional negative dice for melee called shots, because to land that called shot, you have to expose yourself more to make such a precise strike (sacrifice defense, increase risk). With a ranged attack I wouldn't add any additional Neg dice.

IMO, a called shot doesn't expose you to anymore risk or potential stress (except in melee) so no greater risk of Trauma, it's just more difficult, so more successes necessary.

As for the truck, I'd just narrate the damage to it as a part of the story, once you think he's exhausted its use, tell him so. Not everything needs to be mechanical. As for realistic reckonings of how many bodies he should be able to smash - all depends on speed. Hitting just one person/zombie at speeds greater than probably 50mph could bust a vehicles radiator, causing it to overheat and shutdown in short order. However, you could probably hit dozens of ppl in the 25-35 mph range and only sustain cosmetic damage. Note this is for a truck, a car could do much less. The real danger for any vehicle in plowing through a crowd is getting high centered on corpses

Sorry Kobato, I wasn't aware of what a kukri is.

In general, I would simply tell them to roll dice as normal, but - if they successfully rolled doubles then they achieved their goal; if not, they struck the body, neck, or lower face.

Shooting is difficult, and for anyone who hasn't handled a firearm in a stressful situation it's doubly so. Shows like The Walking Dead where inexperienced persons net headshots time after time is very hard to swallow; to that end, I don't think the rules need to change much to accommodate a realistic representation.

With firearms at my table if they sacificed movement for a called shot I'd be tempted to give 1 posi die for that, then as above posters said for melee one posi for "aiming" and a negative die for the stress of "standing still not being a sound idea"? I am still ironing out some of these details as well.

I've been running it like this: if a player declares that he wants to aim for the head, then I tell him that he must roll 3 or more successes; if he rolls 2 or less, then his attack misses entirely and no stress is inflicted; alternatively, if any character rolls 2 uncancelled, paired successes on an attack that hits then they hit the brain by luck and destroy the undead immediately.