I flinched really hard too during that scene, yikes! Personally, while I know that animals are still very important in experiments for different reasons, I do agree with Izzy in this particular case that it wasn't necessary, they have plenty of machines for that. They also have lots of patients arriving daily who they learn on, that's sort of the point of being a resident first.
I love that Izzy and Alex are "going steady"!! And I'm very happy that Mer and Der seem very mature and happy. This literal pandora's box of diaries is going to be verrrrry interesting though