You know, then again, we do see the ThunderCats in conflict with the mutants -- sans Ratar-o -- at the destruction of Thundera. So it's not like the conflict began on Third Earth. Maybe I'm grasping at straws here, but again, it could be construed that Ratar-o is telling Vultureman that Slithe would've been wise to call on him back when Thundera still stood. I dunno. I think it might work. But feel free to ignore.