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Always ensure that both parties are comfortable with the intensity of the activity. Never force, coerce, or ignore a partner's boundaries.
At its core, tickling submission is a practice where one partner (the sender or tickler) induces involuntary physical and emotional responses in another partner (the receiver or ticklee) through tactile stimulation.
Some "interesting" long-form blog posts delve into the science and philosophy of this sensation: Knismolagnia