For a minute, I wondered whether Sir David Attenborough might have been a consultant on this. We meet two hand-knitted creatures that looked to me as if they would have been perfectly at home deep in the depths of the ocean. That, too, might have explained something of the eerie darkness that besets them and makes this really quite a sad depiction of what happens to love when it meets something it cannot combat. It’s astonishing how effective and emotive the “facial” features are here, and as the story advanced, aided by a soundtrack that effortlessly substitutes for dialogue, I thought this…