He's almost surprised – had almost expected Tarn to earnestly loose a blast from his fusion cannon straight at his head, almost – but the evidence of the kind of spark-deep power he still holds over Tarn and those like him is hardly news to him. What it is is a stark reminder of what his defection really means, and as Tarn's cannon begins to power down Megatron doubts more than ever that it's a responsible, sustainable decision, for all that it might have been the best he could do in the circumstances.

Either way, though... the best he can do in this circumstance is to seize the end of Tarn's ludicrously oversized gun in his hands while he's preoccupied with his inner struggle, and lift his foot briefly from Tarn's chest to bring it down hard on his arm instead, pinning it to the ground as he begins to pull and twist at the double cannon in a slow and painful attempt to wrench it straight off Tarn's forearm.