I've often read that one of the biggest complaints regarding design in D&D is that a house cat will kill a first level commoner most of the time. Well I happened across the stats for a cat in the back of my Monster Manual for the first time today and... I'm not entirely sure I understand how that's possible.
Let's assume a household encounter with ideal conditions for the cat:
1) the cat has +0 BAB, same as the commoner
2) do NPC classes not get max HP at level 1? The book says to treat them exactly like any other class. Oh well, even without that a commoner will average 2 hp, same as the cat
According to the monster manual, cats prefer to sneak up on their prey. So let's say it's midday, the commoner is working in the kitchen preparing food, and the cat sneaks up behind him and prepares to strike. The cat has a superior Hide check, (even on a 1 there's only a 30% chance it will be spotted), but with a +6 to Move Silently, he only has a 40% chance of not being heard by a particularly inattentive owner with no ranks in listen (35% chance against an average one), but let's assume he catches his owner unaware.
For the cats surprise round, it executes a partial charge for a +6 to hit with his claw attack. Against an average commoner this gives it an 80% chance to connect for 1 point of damage, and a 5% chance of a critical hit for 2 points of damage. In either case it has zero chance of dropping the commoner before combat begins, and an exceedingly low chance of putting the commoner in significant danger, so let's assume the cat connected for 1 point.
The owner turns to see what is clearly a feral cat, and, armed with a kitchen knife, prepares to defend himself. The cat has only a +2 to Initiative from its Dexterity, giving it a 10% chance of going before the average commoner. Assuming the cat does win out, it can proceed with it's full attack routine: two claws at a +4 and a bite at a -1, the claws have a 75% chance of hitting and the bite has a 45% chance and the cat must succeed with at least two of these attacks in order to incapacitate the commoner before he has a chance to retaliate. Discounting critical hits, it has roughly a 78% chance of doing that. Good odds, but certainly not guaranteed.
However, assuming the cat does not win the Initiative roll:
Since the cat is a tiny creature with a reach of 0 ft, it must enter the commoner's space in order to attack it, and it does not threaten adjacent squares. If the commoner wins initiative, it takes a 5-foot step away from the cat and attacks it with the knife. With his BAB of +0 he has a 45% chance of hitting the cat's modified AC of 12(the -2 from charging doesn't go away until the start of the cats turn). If he hits, even with an average damage roll of 2 the cat is immediately disabled: it moves at only half speed and it can only take a single move or standard action each round, and any standard action puts it to -1 hp.
But let's assume the commoner misses. Since it is too close to charge, the best the cat can do is move in to attack. Entering the commoner's square provokes an attack of opportunity, with a 35% chance of success to once again incur the penalties above. So even with surprise, only 1 round after losing initiative there is about a 50% chance the cat has been disabled and a 5% chance the commoner has been.
Now granted, an unarmed commoner the odds shift more in the cats favor. But I would be more surprised to find that going up against a creature with natural weapons when you have no weapons of your own resulted in anything else. The instant the commoner picks up even an improvised weapon it becomes far from a sure thing. In an actual D&D game, with all the myriad of possible mitigating circumstances, I find it very unlikely that a house cat that randomly attacks it's owner would win.
...Am I just thinking about this too much?