[57] Which, on that occasion, is lightness of the mental body (kāya-lahutā)?
That which on that occasion is the lightness, the capacity to change quickly, the absence of sluggishness, and the absence of inertia of the aggregate of feeling (vedanākkhandha), of the aggregate of perception (saññākkhandha), and of the aggregate of volitional formations (saṅkhārakkhandha) — this, on that occasion, is lightness of the mental body.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.