Thane's determination to kill Sif is strange to Thor. He's too used to people quaking in fear when he yells, and he's certainly not used to being ignored when he makes a violent approach. He doesn't know what motivates Thane to pursue her, but he cannot allow it to happen.

"I will." He confirms darkly, brows furrowed and eyes frantic as he fires the gun several times at the alien. It's a strange weight in his hands and he doesn't much like it. He wants his hammer. The urge to throw the damn weapon at Thane's head is high, but instead he'll try to throw himself at him and knock him aside. Thane is already too close to Sif, Thor isn't as fast as a man smaller than him would be.

But he will not give her up without a fight.