How could a Pitbull bite off someone's arm?
It's not inconceivable.
(not defending the cartoon or making any sort of point re: banning pitbulls)
People have no idea of what
small dogs are capable of if sufficiently provoked, poorly bred (or properly bred but in the wrong environment), and/or poorly handled.
Let's take the Jack Russell Terrier. They are energetic, intelligent, playful, and just generally fun dogs. Once trained, they enthusiastically do as they're told. This breed is a very expressive people-lover. That's the good side.
The bad side? They're terriers! They are bred to kill rodents and other small animals (not bad in working lines, but a real problem in others), and they end up in vet hospitals ALL THE DAMN TIME for attacking larger dogs. Their exercise needs are pretty high, even for an athletic owner, and become very destructive if not exercised. JRTs are well-known as escape artists, are infamously difficult to train, and terrible with small children (because they are highly reactive, rather impatient, and respond right away to a 'threat' or 'prey'- in other words, they are biters and in some cases maulers). These dogs have injured (and killed!) children and pets, even those they've known their whole lives.
Are all JRTs, or indeed are all terriers this way? Is owning one like having a time bomb in your house, or a tiger? No, but if we're talking about one with behavioral issues, this is usually what comes up in that type of dog.
Guess what? Pit bulls are really big terriers, with the added bonus of being really popular with exactly the kind of person who shouldn't own any kind of animal.
(No, I don't believe in banning breeds... But potential pit bull owners had better be prepared for that terrier personality -good and bad!- or it's not going to be pleasant for anyone).