Tickling is usually thought of as play behavior, but not everyone likes it.

Laughing and smiling don't always indicate positive emotion.

Tickling, and the laughter and squirming that results, may have evolved to help protect us from attack.

Is tickling simply playful behavior or is there more to it? In another example of how we are all different, many people interpret tickling as an act of aggression or interpret the tickle as painful and not play at all. And yet, these same tickle-haters likely behave as tickle aficionados do, smiling and laughing when tickled. So, why do we tend to respond with signals that usually indicate positive emotion, even if we don’t like what elicited them?

Humans smile when they are amused, but also in very different, even negative situations. Harris and Alvarado (2005) asked people about their emotional responses to three different conditions. First, being tickled. Second, listening to a recording of a comedy sketch and third, having their left hand immersed in a cold-water bath (a painful condition that the participants endured only for as long as they wanted to). The researchers also recorded the facial expressions of the participants in all three conditions. Finally, the participants were asked about their emotional response to each of the conditions and if they enjoyed being tickled.

About a third of the participants (32%) said they enjoyed being tickled, another 32% had a mixed reaction to it and about 36% said they did not like it at all. When they compared facial expressions across the three conditions, both tickling and listening to comedy elicited a true “Duchenne’s Smile” – an upward turn of the lips and crinkling of the skin around the eyes – the kind of smile that is usually taken as a genuine indication of positive emotion. Non-Duchenne........

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