"Let me think," said Jamie. "I got it! I wish that until me or Jon reverses it, Karyn would be female and male twins named Karyn and Kevin, who look about as identical as me and Jon. You can try being like us for a while."
There was suddenly a fourth person standing in line--a boy with brown hair next to Karyn--or more exactly, Karyn's position had been replaced by two people, both similar looking and of opposite sexes.
Karyn and Kevin looked at each other. Then Kevin turned to Jamie and said "Wait a minute! This isn't the same as you! You two have your memories, you each remember being yourself. I don't remember anything about being this Kevin guy, so it's much harder for me!"
"I remember myself," said Jon, "and Jamie remembers herself, but we each remember ourself as the only one. We don't remember there being two of us. So we do have memory holes."
"But," added Jamie, "if you want me to arrange it so you only remember being Kevin, Kevin..."
"Uh, no, that's all right!" replied Kevin.