Kxitty warriors are in Astounding Planet and in Ringworld, the latter made by Larry Niven. They have 16 hearts and are the second enemy in Astounding Planet. They have claws (Void claws, damage), can summon a spaceship (War strike, burn), and their roar turns Lex (or you!) to stone (Lion roar, petrify). They are like bipedal big cats, and are thus unable to resist a big enough ball of yarn.