The PCs in my campaign haven't eaten many meals yet, but in the last session they had a few to remember.
The inn's serving woman brought them their meal, a simple lamb stew with bread and cheese, and they started to eat. Almost immediately they had to make fortitude saves. Two of them failed, vomited, and then fell unconscious.
Most would assume they'd been poisoned.
One of the unaffected PCs carries the afflicted characters to their beds then returns to the dinner table. Unbelievably, he asks if the two PCs who got sick finished their meals. Finding their bowls half full, the glutton finishes what they left behind (and makes his saves again).
Everyone is ok the next morning. The same woman (someone in disguise, who wants them dead) serves them, and again they have to make saving throws. One of the same PCs who were affected the night before fails again, gets sick, and is out cold.
Don't worry about wasted food though; the gluttonous PC finished the food again...
They never did suspect the woman serving them. They barely seemed to think that poison was involved.