No, I don’t mean just complain about your lack of homework, I mean a sort of low, wordless, drone that sends shivers up your spine. If they moan, the chance that they are a zombie is pretty high. However, moaning alone is not sufficient reason to take offensive action against the teacher. Some teachers, especially the most veteran of the breed, have given up using normal language on the basis that the bloody students never bloody listen any-bloody-way, god I don’t know why I bloody bother, I really don’t, uuuugh! Mumble, mumble, mumble, gnumph. Like that. A pretty good test is to ask if you can go to the toilet. If they just moan threateningly and incoherently at you they are probably not a zombie, but if they lurch over and try to eat your face, then either hit them with a chair or run very fast.