Symbolism, Imagery, Allegory
Atufal is shackled in some pretty intense chains and an iron collar when he refuses to ask Benito Cereno's pardon. This is weird for a couple of reasons: supposedly, all of the slaves are play-acting to avoid making Captain Delano suspicious. But the rest of them seem totally at ease walking around the deck without their chains on. Also, Atufal is Babo's right-hand guy. If anyone on board should be free and proud, it would be Atufal.
But then again, Atufal's actual freedom is pretty temporary. We don't really get to hear much about his fate, but we can assume that he never made it to Senegal. The iron collar he wears seems symbolic of the elusiveness of freedom, even though he's just pretending.