Walking around barefoot gets all sorts of filth onto the bottoms of Katrinas feet. So this slave really needs to work his tongue overtime to get it all removed. Katrina doesnt have all day, but she stands there patiently while her slave does his best to clean her feet before she goes inside. She looks down at him as he works, judging his performance and likely deciding how painful his next whipping will be based on how well and with how much enthusiasm he licks the filth off her feet.