奴颜婢膝 is formed by combining two compound phrases: 奴颜, meaning "slave's face", and 婢膝, meaning "maid's knee". Here, 奴 and 婢 refer to servile individuals, while 颜 and 膝 denote body parts, face and knee, respectively. The pairing of each person with a body part creates a literal depiction of submissive gestures, which together convey the metaphorical meaning of fawning and servile behavior.