Best tummy/navel tickling that you have seen or experienced?

The feet and armpits might be good tickle spots, but the torso is where it is at for me. Back in high school biology class the teacher had this box we could slip science questions into and one was about why we are ticklish. Apparently for the sides and stomach or ribs it's because we have all our vital organs there and it's sensitive and it makes sense. Plus you have the belly button which is basically a landmark for people's devious fingers. Anyone have any great experiences or things they have seen?