Underwater Jokes! (Tickle Scene in "Lost" S1X12)

Laughing is a spontaneous and beneficial behavior for the body, but there are situations in which it is definitely better not to open your mouth to give vent to this natural urge. 

Kate knows something about this, as we see in "Lost" (season 1, episode 12).

Kate and Sawyer dive into a lake at the foot of a waterfall.

Sawyer swims up to her and tickles her with his hands at her sides.

The girl, caught off guard, smiles but tries to keep her lips together. Sawyer continues to tickle her and she is forced to shoo him away and back away as fast as she can, to avoid laughing and thus lose air.

There are times when it is good to laugh, but this is not the case!

Tickling in Lost

At this point in the series Kate and Sawyer are not very close: the woman is suspected of lying to the rest of the group, and the man appears selfish and antisocial.

In this scene Sawyer seems to want to get closer to Kate. By tickling her as they swim on the one hand he reduces the distance between the two of them. Tickling her belly and making her laugh may force her to resurface to breathe. However, the woman seems to smile because she is amused by the joke and does not appear threatened.