Mad-Eye/Crouch demonstrated Avada Kedavra on a spider in Book 4, and nobody had a problem with that (besides some of the students, who were appropriately shocked). I assumed that this is how Quirrelmort will teach it here.
Incidentally, he also (next chapter) demonstrated Imperio on students, teaching them to overcome it. He got (or so he claimed) permission from Dumbledore for this, although I don't know why Dumbledore had the authority to give such permission. He also gave them the opportunity to leave first, but taunted them so that they wouldn't.
Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread: