[SamBam]

But pain is subjective by definition. What does "imaginary pain" mean? The answer can only include some notion of "cause."

[foldr]

Imaginary pain is pain in your imagination, just like an imaginary car is a car in your imagination. If you stub your toe, you are really in pain and not just imagining it. If you imagine stubbing your toe, you are only in imaginary pain (assuming that you imagine it to be painful).

[SamBam]

Precisely. You brought up cause (stubbing your toe). You're agreeing with me.