The dumplings contained insecticide.
This is only the most recent report in a long, depressing, and frankly terrifying list of dangerous Chinese-made food products.
Moral of the story: Please don't eat food imported from China!
Oh, this is a terrible tale, isn't it? I'm very fond of dumplings. The best ones, though, are really the ones you make yourself (start with ground pork, minced water chestnuts, lots of green scallions, LOTS of fresh ground ginger... and NO INSECTICIDE PLEASE.)