Tap Into This

The tap code, or knock code, goes letter by letter
To tap out a message. In some ways, it’s better
Than Morse code: It’s easy to learn on the spot,
And using percussion is usually not
A good way to note when a signal is long
Or short, so the listener might get it wrong.

The tap code involves a Polybius square,
A five-by-five grid with all letters in there,
Except for the K, which the C can replace.
(Alas, that means “fake” would be turned into “face.”
If I were designing, I’d take out the Q.
I’m sure that would spell less confusion; don’t you?)

You first tap the number of times for the row
And then tap the one for the column to show
Which letter you mean. For example, the C
Is signaled by one tap, a pause, and then three.

My sources don’t say how far back the code goes.
It’s likely a secret that nobody knows.
But nihilist Russians imprisoned by czars
Reportedly used a grid different from ours.
The Anglosphere used it in World War II.
The Vietnam War’s when it really came through,
As four POWs held in Hanoi
Discovered the tap code was best to employ
To keep up morale and the chain of command.
If next to each other while talking was banned,
They’d tap someone’s thigh or could sneeze, sniff, or cough,
Until the guards noticed and cut them all off
With more isolation and thicker cell walls.
They still found a few ways when walking the halls.

The tap code turns up in some video games,
Books, films, and TV shows (I won’t say their names).
If I’m ever locked up or silenced by force,
I’ll favor the tap code. Apologies, Morse.