my baby Corn used to do that - the tail rattle thing (and it used to strike constantly also), still does rattle sometimes. i understand why my baby Corn does it (it's a baby and it thinks i'm a huge predator) and they grow out of it.
why would an adult Corn do it? not sure. did your temps change? it is winter/colder and maybe the lower ambient air has caused it to go into brumation? and your attempt to feed it, disturbed it and it struck out.