We must consider some of the facts when we read through this song. First, because the box was floating in the bay presumably he gets wet when he goes to pick it up. Second, it helps to know that it was in the bay and not in the open sea. A few questions come to mind at this point. 1. When he picked IT up in the second stanza did he pick up the BOX or the THING? 2. Why did he need to run? 3. Was there only one cop on the police force?
By the second stanza we know he didn't take the box, only the object in the box and that it can be recognized at a distance. Line 3 of the second stanza make that clear because it states " and this is what he said to me as I walked in his shop, Oh get out of here with that… before I call the cop."
The third stanza suggests that he has put the THING down because he picks it up. Why did he put it down? Was it heavy? Why was he running for his life? Why was his wife so offensive saying "...and don't come back no more?" Is he cast out?
In the final stanza readers are warned not to pick up a wooden box if by chance you see one at the beach, but isn't the problem what is IN the box? Also the song says that whoever picks up this THING would "... never get rid of that... no matter what you do?" Does two attempts to get rid of IT justify "never?"