Skin the cats are a great measure and developer of shoulder flexibility, strength, body control, and spatial awareness.

Start hanging from a bar (or rings). Keeping the arms and legs straight, lift the toes to the bar, continue through a basket position, and lower yourself over into the "skin the cat," rolling all the way through to an "eagle" grip if shoulder flexibility will allow. Eyes forward, not down at the ground. Then, from the bottom, pull back up and pass the legs forward through the arms to return to the original hang position.

Obviously, warm up thoroughly, take this slow at first, use a spotter, and make sure you have an exit plan. Practicing on low rings over crash mats would be a Good Thing.