The hole/tunnel in Captain Verdeterre’s Plunder

Have anybody figured out how to deal with the hole/tunnel in Captain Verdeterre’s Plunder (‘a. u. u. u. listen. x tunnel’)? I’ve tried inserting various things, shooting down the hole, crumbling the hardtack in the hole, speaking into the hole, asking the captain about the hole, playing the zither or the violin, putting the captain into the hole (he doesn’t like getting picked up) and using the mirror to look down the hole, all to no avail (and not all of these actions are actually implemented). Is it perhaps just a red herring?

Not a red herring, just lousy design. I apologize.

“>look in hole” is the command you want. It was not cool of me to rely on the player knowing that Inform treats “looking at” and “looking inside of” as separate concepts.