Well, that definitely wasn't the ending anyone was expecting. Dexter ended its 8 season run on Showtime last night, going up against the Emmy Awards and the penultimate episode of Breaking Bad with a series finale that left some both outraged and confused.
All sorts of foods contain onion, including baby food. You might not realize that your dog is eating onion or garlic in certain snacks or table scraps. Symptoms include vomiting, diarrhea, drooling, rapid breathing and heart rate, abdominal pain, appetite loss, mouth irritation, dark urine, lethargy and pale gums.
Cats are probably a little more sensitive to onion toxicity than dogs are. I can't find an exact quantity of onions required to cause toxicity problems in dogs, but there are several case reports of onion toxicity and they involve whole onions or sizable portions of chopped onions (like a cup or more).