When I have pictured John the Baptist untying Jesus sandals or Jesus writing with his finger, I had thought they were squatting (cf. ὀκλάζειν "squat", bend the hams and go down). Have I been mistaken? Let me spell out the steps I have taken so far on the path of self-doubt...
Our Italian friend (page 219) gives κλίνομαι = κύπτω. While they certainly are similar, I think κλίνεσθαι implies that there is something to lean against, while κύπτειν means bend only supported by ones own strength.
Hippocrates when speaking of a curvature of the spine laterally says καὶ ἐς τὸ πλάγιον σκολιοῦνται σπόνδυλοι. That is to say that the σφόνδυλοι "vertebrae" (Attic spelling of σπόνδυλοι, which is described as being Ionic and Later Greek) are curved (cf scoliosis), but that is not referred to directly as κύφωσις (described in LSJ as being hump-backed). σκολιοῦσθαι is used to describe the general curvature of the spine (ῥάχις , ιος, Att. εως, ἡ). Since Hippocrates compares κύπτειν to the lateral curvature, it is likely that κύπτειν only (or at least usually) refers to forward movement.
The passages in question are:
Mark 1:7 wrote:Καὶ ἐκήρυσσεν, λέγων, Ἔρχεται ὁ ἰσχυρότερός μου ὀπίσω μου, οὗ οὐκ εἰμὶ ἱκανὸς κύψας λῦσαι τὸν ἱμάντα τῶν ὑποδημάτων αὐτοῦ.
John 8:6 wrote:Ὁ δὲ Ἰησοῦς κάτω κύψας, τῷ δακτύλῳ ἔγραφεν εἰς τὴν γῆν
John 8:8 wrote:πάλιν κάτω κύψας ἔγραφεν εἰς τὴν γῆν.