A mirror, a speedster, a killer, a vane To know these is to know my name

Lives in a box, with no key Soft, and light as can be. Comfort a nose when a cold makes you blue Jumps into action when you say achoo

I rock without rhythm, yet lullabies start, I hold the smallest cargo close to the heart. I travel no distance, but journeys begin, Where blinking new eyes first take the world in. I’m empty by day, at night softly filled, With dreams that are borrowed and futures yet built.

Sometimes I feel invisible but I know I’m sharp. It’s funny-we share a feature but you keep me away from yours. Some pass through me, some can’t find me and some can’t move me. What am I?

I dance with blades both sharp and bright, opening wide, then closing tight. Two partners moving side by side, to part what once was unified.