John Higgins' Bridge Hand

[gettingbetter]

I've seen Higgins do something odd with his bridge hand on certain occassions. I'm not sure if he is the only player to do so. What he does, and I think this is usually when he is pretty close to the cushion, but bridging on the table bed is that he depresses his index and middle finger - as you would for a screw/stun shot but he will have his ring and pink finger in a pose that is akin to playing a shot with top spin.

Does anyone know why he does this?