Blood from the gash on his head – which was his father's first effort – is trickling across his face. Add to this, his left eye is blinded; but if he squints sideways, with his right eye he can see that the stitching of his father's boot is unravelling. The twine has sprung clear of the leather, and a hard knot in it has caught his eyebrow and opened another cut.
(Wolf Hall by Hilary Mantel)
Does the bold part mean that the twine from the leather boots is flying away or broken and the boy on the ground is kicked again?