I think onions are toxic to cats, also. All members of the lily family, if I'm not mistaken.
All right, here's a story for grown-ups only. My S.O.'s band (who are all from various points in the Bible belt) came to play a gig in my hedonistic hometown of Ithaca, NY. Well, there's an organization in Ithaca that promotes safe sex by giving away little goodie bags containing chocolate and condoms. They're often in the downtown shopping district, handing out these bags.
Well, one of the guys in his band grabbed a few of these goodie bags, because he thought it was pretty funny that they gave away condoms in a public area (not so common in the deep South). He left them on the table, and Mom's dog (the canine vacuum) naturally ate them. After calling the vet and getting reassurance that the dog would survive just fine, and we should just watch her carefully, Mom thought it was pretty hilariously funny. The guy was actually scared to tell my Mom at first, because he didn't want to offend her.... little did he know that my Mom is a big supporter of the organization that gives the condoms away.
This dog has eaten plastic grocery bags, playing pawns from board games, an entire jack-o-lantern, a scrunchie.... every random object you can imagine. Once they even had to take her to the vet because she'd eaten a bag of onions, and while they were pumping her stomach, they found a plastic baggie, a spool of thread, and a few other bizarre objects.