Blood flow

What you're seeing

1. The camera travels along the inside of a red, ridged tube, looking down its length towards a brighter opening.
2. Red discs tumble past in large numbers, with smaller grey, textured spheres carried among them.
3. Some discs pass so close to the lens that they fill much of the frame and blur.
4. Near the end a pale, glowing sphere drifts by in the foreground as the camera keeps moving forward.