When people know his nervous ticks, at least.
Tyson's default nervous tick is a slight twitch in the first two fingers of his left hand. Try it now: with your hand open, twitch those first two fingers. Which ones moved? The answer should be your index, middle, and ring finger; due to the ring and middle finger sharing a tendon. When Tyson lies the ring finger of his left hand twitches.
See how easy it could be to think he's lying now? Especially because he's already displaying nervous behavior, which can be a sign of lying.
So, why isn't his default nervous tick listed as all three fingers moving? Well, when his nervous tick happens and his hand is closed, it's only the first two fingers that move.