I'm teaching some of my friends magic, and morph seems to be a bit of an outlier mechanic. It's one of the few things that a player has a choice to do but 'doesn't use the stack'. It can make it a bit hard to describe to my new players that are just learning how the stack/abilities resolving work.
Is it fair to describe morph as a cost (paid in addition to the actual morph cost), which does nothing? Effectively, rewording it as
[Cost], turn this creature face up: Do nothing.
Of course, once a creature is turned face up there are effects, such as a change in the creature's power and toughness, and (usually) triggered abilities, but those are only a consequence of an action happening, not a new action paid for by the morph cost.
In my understanding, treating morph as a cost in this way is entirely keeping with the rules. As normal costs, it can only be done when you have priority. Similarly, it can't be responded to. (A creature sacrificed as a cost, as an analogy, cannot be responded to either.)
My question is: is this a fair way of explaining the special case of Morph as a mechanic to newer players, or is there some rule or corner case that I'm missing?