The mouth is spoken of as an organ of action because it contains the instrument of speech, and that of eating. The feet are organs of locomotion and the hands for doing various sorts of work.
जल्पनाभ्यवहारार्थं मुखमिन्द्रियमुच्यते। गमनेन्द्रियं तथा पादौ कर्मणः करणे करौ॥