It really depends on the circumstances and how Dean reacts; if he can’t see anything because it’s dark, and he hears Sam’s voice (no matter how loud and how distorted), he’s not going to strike out with gun or knife until he knows where Sam is and what’s going on. If it’s light out and Sam catches him off guard, he might get a cut on a finger from Dean lashing out instinctively.

Much figuring things out would happen afterwards, along with really big, hurt eyes from Sam if he got stabbed. oAo