When the IOU lands on the lamp it is projected onto the ceiling. However, if the message was written on normal paper, which is most likely, the projection would have just been a solid square rather than the message. See more
Try to be nice to my sisters. It's very hard on me to have you fighting all the time.
Oh, OK Marge, I'll get along with them. Then, I will hug some snakes! Yes, I will hug and kiss some poisonous *snakes*!
Now that's sarcasm.