This pair of images caught my eye as I was flipping through my psychology book. I just had to share them with you guys to find out whether I am the only one who, well, you'll see. The images are used in language experiments with toddlers. The toddler sits on their mother's lap in front of the two images, like TV screens, one depicting Cookie Monster tickling Big Bird, the other Big Bird ticklng Cookie Monster. A message is then played saying either, "Oh look! Big Bird is tickling Cookie Monster," or "Oh look! Cookie Monster is tickling Big Bird." Hidden observers record which image the child turns its attention to. The point is to see whether the kids look at the image corresponding to the sentence they just heard (and by inference, whether they understood the sentence). What I want to know: What exactly do they mean by 'tickling'?