Partridge (233) gives us a clue. He defines a pew-opener’s muscle as one in the palm of the hand “because it helps to contract and hollow the palm of the hand for the reception of a gratuity.” From this we infer that a pew-opener was an impoverished parishioner who was allowed to gather tips by escorting well-heeled worshipers to their family pews and holding the pew doors open for their benefit. (If you don’t already know the word, a pew is an enclosed church bench.)