Rarely there are notes on the same lane consecutively which you should tap repeatedly on one key as fast as you can. I tried tapping on one key with my two alternating fingers.The tapping speed for me is approximately 8 taps per second, which I couldn't do it.
Example
Anyone which has beyond this speed is considered a "machine".
Example
SPOILER
http://osu.ppy.sh/b/156352 played with Nightcore modifier as an attempt.
http://osu.ppy.sh/b/156352 played with Nightcore modifier as an attempt.
Anyone which has beyond this speed is considered a "machine".