Healing Technique

You choose whether to make a copy as the demonstrate ability resolves. This happens before the original spell resolves. Your copy goes on the stack above the original spell.

This means that if you cast a spell with demonstrate and both you and an opponent copy it, the opponent’s copy will resolve first, then your copy will resolve, and finally the original spell will resolve.

If you cast the spell and choose not to copy it, no opponent will get to copy it either.