Compare: 俯す vs 俯す

俯すふす

to lower (one's head, gaze, etc.)

俯すうつぶす

to lie face down (e.g. on the ground, napping on a desk); to lie prone

N3Su verb (precursor to suru)

to lower (one's head, gaze, etc.)

うつぶす俯す

N3Godan verb (su ending)

to lie face down (e.g. on the ground, napping on a desk); to lie prone