The SLASHER-TO-HALO is a kettlebell exercise. Well actually it's a combination exercise that meshes TWO kettlebell exercises: the Slasher and the Halo. It comes to us from Rob Shaul of Mountain Athlete and Military Athlete.
Locally, Joe the Raven turned me onto this movement. It's proven great for warmup routines...with its focus on shoulder mobility and trunk rotation/stabilization.
First start out with some Halo practice. Go in each direction. Watch the video carefully. Rob dropped the KB to his chest after each pass, but you can surely keep rotating it around your melon for reps. Note the KB is handle-up as it passes the nose, and bottom-up when it passes behind the head.
Don't have a KB yet? Try it with a weight plate. Just don't knock your teeth out!