Intent

Ninjas can’t be co-authors. You can’t reasonably give input from the shadows. And sneakiness doesn’t lend itself to cooperation. You never hear about ninja synergy do you? No, you don’t. And don’t get me started on groups of ninjas. Ninjas don’t work together, or in teams. Any multiple sighting of ninjas is either an illusion crafted by a single ninja, or a coincidence. All accounts of ninjas fighting together are actually just instances where several ninjas have the same target and are in reality racing to get the kill.

That’s why sneakily reading over my shoulder doesn’t make you a co-author.