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Laughing when being tickled is a defense mechanism kicking into gear, responding to panic and anxiety.
Laughing when being tickled is a defense mechanism kicking into gear, responding to panic and anxiety.

Tickling requires the other --- you can't tickle yourself
How many tickles does it take to make an octopus laugh?Ten tickles
How do you make an octopus laugh?You give it ten-tickles
How do you make an octopus laugh?With ten-tickles
Tickling is a momentary pain and apprehension of pain with an immediately succeeding removal of these, and their alternate recurrency.
Tickling is necessarily a two-person affair --- It is not possible to tickle yourself
Pteronophobia is the fear of being tickled by feathers.