Lady Betty and her friend Lady Bertie do not like slaves who are not obedient. They had to punish this one for being disobedient. But since he was new, they did not want to go nuclear on him. They decided to try and humiliate him small time. So they spat on his face and even spat into his mouth. They wanted to humiliate him and express their dissatisfaction and by the time they were done with him, he understood.