Snipe for the same reasons you mention but also rails as they flutter up at close range only to dip down below the reeds before you can get the gun to the shoulder. Then they run off worse than a late season pheasant.
Gun shy English sparrows and starlings jumped from the bird houses are also pretty tough- they often dodge behind the bird house when flushed and puts the house at risk. Years back, bats were very tough targets but they aren't legal these days.
Now that I've been thinking, the hardest bird to shoot is a goose outside a metro area with a neck tag. I have seen more of those missed than hit I think. I'm around 50% shooting them but I have a lot of early missing to make up for. Others percentage when I've been around is much lower. If it was 10% I would be surprised. It is the worst causation of "buck fever" I have seen.
Snipe!! They are the toughest bird to hit I've ever hunted. A fast snap shot is the best way to connect, IMO. They fly straight for the first 20 feet.
