If Wikipedia is to be trusted,
The shoe represents the lowest part of the body (the foot) and displaying or throwing a shoe at someone or something in Arab cultures denotes that the person or thing is "beneath them." Showing the bottom of one's feet or shoes (for example, putting one's feet up on a table or desk) in Arab cultures is considered an extreme insult. Examples include Iraqi citizens smacking torn-down posters of Saddam Hussein with their shoes, and the depiction of President of the United States George H. W. Bush on a tile mosaic of the floor of the Al-Rashid Hotel's lobby, forcing all visitors entering the hotel to walk on Bush's face to enter the hotel.I wonder if we can connect this to midrashim and or psukim, to grant us some additional insight. There is the famous midrash about the contract between Mordechai and Haman made in the desert:
The two delegates set out on their way to Persia at the same time. As their way took them through a desert they brought with them provisions for the journey. Haman, who was greedy, ate his all at once, while Mordechai allowed enough to remain for the whole journey. Soon Haman became very hungry and begged Mordechai to share the remainder of his fare with him. At first, Mordechai refused his request, but later, he relented on the condition that Haman agree to become Mordechai's slave. As they had no paper to upon which to write a contract, Haman wrote the following pledge upon the sole of Mordechai's shoe: "I, Haman the Agagite, have sold myself to Mordechai as his slave in consideration of bread."
Since then Haman could never forgive Mordechai for his humiliation, and he was in constant dread lest Mordechai enforce his slave claim over him.
Mordechai, of course, never dreamed of doing it. Later, however, when Haman became Prime Minister, and demanded that Mordechai bow down to him, Mordechai would merely remove his shoe and wave it at him. Haman had to hold his tongue and keep silent. The enraged Haman swore he would destroy Mordechai and all the Jews.
The fact that the contract was on the shoe, and the fact that Mordechai showed Haman the bottom of his shoe to demonstrate that Haman was below him could now, perhaps, take on an added significance.
Perhaps it can also give us added insight into chalitza.
Spitting clearly has connotations of degredation and contempt. And the fact that this fame follows him, as bet chalutz hanaal -- this seems to carry the same message. If so, perhaps we can say that loosening his shoe also is some sort of insult, as penalty for refusing to perform yibbum. And this might work well with the role of the shoe as it occurs in Arab culture.