Onions contain a compound which is toxic to the red blood cells of cats. The red blood cells are destroyed and this results in anemia. The specific type of anemia is called 'Heinz body anemia' because the red cells develop an abnormality called a 'Heinz body' which can be seen under the microscope.
Dug, the dog, is easily distracted by ... squirrels (well, he's easily distracted by everything, but especially squirrels). He can be talking (yeah, it's Pixar/Disney so the dog talks) & right in the middle of the sentence, he shouts, Squirrel!. Then he carries on with whatever he's talking about.
Dogs have some real memory but it's only extremely short in its span. Most research indicates that a dog's short-term memory is about 10 to 20 seconds long. This means that if a dog poops in the house, for instance, and you scold him about it 5 minutes later, he won't associate the scolding to pooping in the house. He'll associate the scolding with you and pooping in general.