I do poorly on almost all 3D targets that have a low, wide body shape such as lying down deer, alligator, etc. I think the brain sees the larger and more "normal looking" body rectangle represented by most deer, bear, hog targets etc. more frequently and considers them to actually be "normal". Then when it sees the odd looking, low rectangle body shapes, it freaks out a bit, thus making it harder to concentrate on a given spot. Yeah, the standing bear presents issues, also. Don't even get me started on turkey targets.
On live targets the hardest shot is always the one I am currently trying to make. Sometimes I tend to over think, even at modest distances.