A reed warbler, to ask them why on earth they quite often stand by and watch as cuckoos lay eggs in their nests; and whether they actually realise that all their chicks have gone and they are feeding a monstrosity in place of them! I know the scientific answers to this question, but I'd just like to know how they actually feel about it! And a trout, to know why, when you have tried every imitative marvel of modern fly tying in your box, a trout will take a bit of chamois leather that looks like nothing at all, tied haphazardly onto your hook. Beats me!