From your quote I wouldn't like to surmise what is happening in that specific excerpt. However a sponge bath is when someone is too ill or infirm to get out of bed to take a bath. A nurse or someone similar has to clean the body of the person in the bed by turning them onto their side and give them a 'sponge bath' using a bowl of water, a sponge and, of course, a towel.
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