It is a fortress.

With strong, high, adamant walls,

A deep, impassable moat, no way across.

The drawbridge is raised, the portcullis is down –

There's no way in.

In the middle of the fortress there's

A room, guarded by four soldiers.

Towering men, plumed helmets, tall shields, long swords –

And inside the room, there's what they're guarding.

A box.

Just a very small box.

It looks unimposing, but it's welded shut and padlocked three times.

Does it hold glittering treasures, plundered from a foreign land?

No. That's not why it's here.

If it's anything like treasure

It's a rare, wild animal.

It's not here so noone can take it.

It's here so it can't get out.