In COD Black ops Zombies the difference between Sickle and bowie knife ?

Ok so in Call Of Duty Black ops Zombies mode you can bye a bowie knife of the wall and in the first strike map pack Ascension you can bye a Sickle instead of the Bowie knife, know while you using the knife you aim at the zombie heart and melee your character will not slash but Stab it but what will your character do since the Sickle doesn't have a straight edge blade ???