Hodu = Hodu Lashem
Cush = cush in well, you know.
Hodu therefore refers to the mouth, which is in the head (elu pinu malei shira kayam…ein anachnu maspikim lehoidois)
Cush refers to something else that is round, albeit bifurcated.
Whichever way you look at it, Hodu and Cush are both related to round.
Therefore, the world is round.