Worshipping a big girls feet is the ultimate possibility for a slave to show his lady his submissiveness. Licking her bare feet - clean or dirty - massaging her soles and toes with his tongue to comfort her. It's the slave's responsibility to comfort his mistress, comforting her feet while she relaxes on the couch, talks to her friends or just enjoys the treatment of her feet.
It's also his job to clean his lady's big shoe collection and clean the shoes immediately when she comes back. Licking all the street dirt from the shoes - witnesses of the lady's walk over the day. He has to lick the shoes clean until they look like brand-new or he risks to be punished by his mistress!