Board Thread:General Discussion/@comment-31926729-20170618102307/@comment-25375217-20170618204408

When did Emma eat a sleeping curse? Regina tried to get her to, but Henry ended up eating it instead and knew what it would do. That doesn't prove or disprove the function.

I suspect the "must be willing" thing is specific to the Poisoned Apple. I seem to remember someone who read Regina Rising saying that it was poisoned before Regina learned about the Sleeping Curse from Maleficent (which raises the Sleeping Curse/Dark Curse trade into question, but that's another topic for another day) and, as Lola said, we've seen a forced Sleeping Curse in later seasons.