The way his eyes work is that he can change color to control different parts of the brain. If you read the bio he can change a persons emotions with one color and read through their brain and esentailly everything about them with another(Merlin's character liam referred to it as soul gazing)  he has a currently unstable power which is the color of red eyes and it allows him two do the afformentioned powers with ease. Which allows more control of more things. which inherently allows the ability to read a movement. Because realistically you think something before you ever say it including every move you make. 

[@Hitman5455]