This. If–IF–it was Emma, then I’m betting she and Henry are currently sharing a heart.
IF she was even able to take Henry’s heart. Remember, Regina cast a protection spell over it specifically so that nobody could ever take it again.
If Emma scarified Henry’s heart, she would likely only have done so if Henry willingly removed his own heart to give to his mother, believing she would save him. Otherwise, maybe Lancelot and Gwen are currently sharing a heart.
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy