Because aliens from the moon. Or, alternatively, either Eirin said that last bit out loud or it was purely for comedic effect. I'd prefer the first answer, myself.
Eirin said aloud that she was going to curse Udonge in the last panel of the previous comic.
SighEven though I visited the shrine at night to put a curse, will it really work?Master.
I'm back from selling the medicines.The curse is working!?Clatter!Guhack!!Eirin, that's just Tewi's prank.Idiot...
She fell for it so perfectly again. ♪Dong!