«كُلٌّ فِي فَلَكٍ»
Each is in an orbit.
Ignoring vowel marks, the sequence is ك ل ف ي ف ل ك. Reading the letters in reverse produces precisely the same sequence, ك ل ف ي ف ل ك. This makes it a compact and transparent example of reversible wording.
The device is not merely that “kull” and “falak” sound related. The symmetry spans the selected expression, including “fī.” The meaning of motion in an orbit adds coherence to the verbal design.