"单手打字" (dan shou da zi, which means typing by single hand) is a common bullet curtain, which is mainly appears in the benefit videos of all kinds of online bullet curtain websites.
Generally speaking, typing is done by two hands when using the computer. Only beginners use a single hand when typing.
But when benefits appear in the video, the man who is typing can only use one hand.
What is the other hand doing? Please use your brain.
Of course the other hand is masturbating.