Leaning forward, you draw forth an elongated and serrated spine that grows from your back, creating a whip of vicious bones in your hand. This magic whip counts as a martial weapon with which you are proficient. It deals 1d8 slashing damage on a hit and has the finesse, light, and reach properties. In addition, when you use this whip to attack a target and score a critical hit, you regain hit points equal to half the damage dealt.   If you drop the whip or throw it, it dissipates at the end of the turn. Thereafter, while the spell persists, you can grow another spinal whip out of your back, causing a new one to appear in your hand (no action required).