If a dwarf's brewing or cooking skill is between 1 and 2, their creations have a 20% chance of causing salmonella or botulism. If skill is less than 1, there's a 50% chance. If the cook hasn't washed with clean water and soap recently, any unfortunate diner has an additional 30% chance of getting sick. There is no way to identify which meals are tainted or poisoned, and they're always displayed as a higher quality than they actually are. No skill is gained from producing tainted food and drink, even though it's shown to increase, and each job will produce double or triple tainted products whenever the player isn't watching.
Also, if dwarves with a herbalist skill of less than 3 pick wild carrots or any kind of mushroom, there's a 30% chance for one of the carrots to cause hemlock poisoning and a 50% chance for a mushroom to cause multiple organ failures for anyone who eats it or a meal made from it.
Any item or workshop made of cinnabar, realgar, or orpiment will give a lethal syndrome to any dwarf who uses it. Toys and food containers made of lead will increase the rate of skill and attribute rust with every use.
Every 1000 steps, the game checks if there's a cat occupying your food stockpile. If so, the most valuable prepared meal with a [FISHITEM] or [IMPLIES_ANIMAL_KILL] ingredient will decrease in quantity by 1 for every cat that is present. If no cat is present, one unit of food will become tainted for every vermin within 10 tiles of the stockpile.
On a similar note, any dog that leaves it's pasture zone will immediately sprint for the most valuable food item it can path to and decrease its quantity by 5 for every 50000 steps that it is loose. After 150000 steps it will also coat every adjascent tile with piles of vomit.