What does John Connor grab between his two fingers when touching the T-101 in Terminator 2 Judgement Day?

After the motorcycle/truck scene, we see John Connor touching the T-101 model to grasp the fact that Arnold really is a terminator. After touching him, it seems like he grips something between is index and thumb. Is this a metal shard of sorts or is he just pushing his fingers together to register what he just touched. I am guessing the black that I saw between these fingers was just oil from his motorcycle?