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Lifting one or both cheeks while shitting to prevent the need to wipe afterwards.
Used first in 1942 in WW2 to prevent undergarment soiling on the field, the cheek lift was and still is widely used to this day.

Lt. Splathers: "Johnson! You shit in the foxhole without paper? I suppose you used your hand that you shake mine with, maggot."

Cpl. Williams: "No Sir."

Lt. Splathers: "WELL?"

Cpl. Williams: "Just a cheek lift"
by JingoBellsSanduskySmells December 28, 2011