There's a pretty fine line between mimicry and acting, and acting that's natural and that which has been rehearsed to within an inch of it's life. I think it's very much the natural that Daniel Day-Lewis delivers here, as does Hugh O'Conor as his younger persona, as we learn of the upbringing of a young lad born with very limited movement and learning difficulties, but a mind that's clearly sharp and a face that's expressive. His family, a typically large one, is headed up by his dad (Ray McAnally) who presents us with a variation on the usual theme of father who comes home from work then…