The dog, who was loathed by the cat whom the mouse feared, barked. Unwound and same meaning as your first and second sentences. Or even simpler: The dog,

The dog, who was loathed by the cat whom the mouse feared, barked. Unwound and same meaning as your first and second sentences. Or even simpler: The dog, who was loathed by the cat who was feared by the rat, barked. Come to think of it, this reminds me somewhat of tail-recursion optimization.