LigPlot+ said that the spooked arcs represent hydrophobic contacts between residues and hydrophobic atoms in the ligand (https://www.ebi.ac.uk/thornton-srv/software/LigPlus/manual2/manual.html), and the default settings is making non-bonded contacts between hydrophobic-any other atom. What I do not understand is why polar residues make hydrophobic contacts too? What is the mechanism for that hydrophobic-hydrophilic contact (what forces, which atoms), and how is that contact contributes to the stability of the protein-ligand complex?