Now for a similar and just as important question, how did Oro get his sword back? Mr monkey man poofed away with it after the third dies.
It's likely that Orochimaru has the ability to "summon" the sword much in the same way ninjas can summon animals. The sword is probably bound to him in some way, and even though Enma took it, it probably returns to Oro every time he regurgitates it.