she identified at least four variants among them , each with specialized functions : crawlers she 'd dealt with during the first wave ; leapers could spring like frogs when close enough and slash out , or worse yet , latch on ; spinners could accelerate at blistering paces for short bursts , becoming flying saw-blades ; the last group was still unknown , trundling more at the rear , slower than the others , looking like steel helmets with legs .