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Grimlock didn't really like Optimus Prime, and didn't care who knew it, but he did serve under him and he would admit (grudgingly) that he was (usually) a good leader. So, when he saw Motormaster creep up behind the Prime with his sword raised while the other mech was fighting a Seeker, he didn't hesitate.
Grimlock charged the Stunticon leader with a mighty roar. It was enough to startle the other mech into brief freeze, which was enough time for Grimlock to reach his side and wrap his teeth around Motormaster's wrist.
The Stunticon screamed as he bit down, a sound that rose in pitch as he tossed his head and ripped the other mech's hand, and part of his forearm, completely off.
Optimus, finished with the Seeker, turned and punched Motormaster in the face. The new injury combined with shock sent him offline. "Thank you, Grimlock."
"You Prime owe me Grimlock." His words were garbled around the arm still clamped in his jaws.
"Indeed I do." Prime nodded and then turned back to the battle.
Grimlock chewed Motormaster's arm as he did the same, waiting until he found another opponent to drop it into the dirt. But he made sure to tuck the other mech's sword into his subspace pocket before charging at the next Decepticon.