footrubbing

You begin to rub her feet. She purred. "You deserve this. After all you did to me recently" he said. "We had to... really... they made us..." she said. "Explain" "Please..." she sobbed. Gently you suck her toe, she giggles. Than pat it. "Alright... but you need to swear something..." "..." she looks at you.

What does she have to swear?