In TF:TM (1986), Unicron used his horns to plow into a planet and pull it into his gaping maw. fast forward.... When he is summoning old Megatron, megatron wakes up and Unicron's "voice" pushes him back, so he grabs at Unicron's horn, and as he slides, he actually scratches the horn's surface. if eating planets doesn't harm Unicron's paint job, then how did megatron do it? just a nagging thought at 6 a.m.