IF the students are not to young, then i don't see why they shouldn't see the killing. First of all the teacher must explain to them the whole situation and the purpose of doing such thing. Must explain that the dog(s) are going to die and that the snake is not a bad creature that loves to kill, but it's just a carnivorous creature that needs to feed. Then, i don't see why the students shouldn't see the killing and they must let to their humanized emotions, continue to imagine theirselves outside of everything that has to do with nature, her ways and the instinct of those animals. It is hard but it is the truth. We shouldn't raise our children so fragile. The real world IS pain among happiness. We ought to show them that part of life but gradually and explaining all their questions.
The fear leads to death as the window to the courtyard...JUMP!