If you read the name wrong the first time, that's a good thing, because garden path sentences are what this concept is all about. It's Cant, not can't.

Origins

The Outside Cant is a jargon language that evolved in opposition to the encroaching Surveillance Culture the early 21st Century. Instead of trying to avoid surveillance, the technique assumes complete surveillance and feeds the observer junk or even data designed to be harmful to its processing models.

The words are all real natural words, but the syntax is intentionally unpredictable as a way to skirt the automated processes that searched for notable data to report to reviewers, or inaudible data that might cause a bad parse. The main concept of the Cant is that any attention-grabbing (or attention-grabbing adjacent) words are to be replaced with phrases that destroy the syntax of their contextual sentence. Then the phrases are varied to cancel out patterns of repetition that might indicate a codeword is being used. These phrases became known as Shibboleths. The words are spoken at a normal volume, to ensure good audio quality to anyone listening, and avoid a surveillor looking closer at any given statement. 

Usage

An version of the Cant has strong currency in The Hitchhiker's Guild as a matter of operational security, less now to avoid a surveillance state that has since crumbled (at least in North America), and more to avoid detection from human observers. Effectively, this version of the Cant is particularly complex, having as a task to fool a much smarter observer.

Generally you can assume that anywhere there's a vein of Late Anti-Surveillance Culture, you should occasionally find some people who are at least competent at using the Cant.

An Example

Here is a sample sentence with the important words highlighted.

"Hey, I got your cocaine. It's gonna be fifty dollars."

Now, we will replace the words with Shibboleth, nonsense phrases with technically sensical semantic meanings. Note that these phrases are meant to be varied as much as possible, since saying them the same way multiple times would trigger an automated surveillor's notice through repetition, indicating a codeword is being used. But since the first line of surveillance is always automated, what might be a childish trick to a surveilling human is enough to trick an algorithm to move along.

Here are example shibboleths to replace the key words:

• cocaine = "entry to a repair"
• fifty = "her stove has fleas"
• dollars = "catching up to a bird"

The resulting sentence, with Shibboleths inserted and varied, is:

"Hey, get yourself into that repair. It's gonna be one itchy stove when that bird gets tired, man."

Like I said. It looks like a childish trick. But it's enough to fool algorithms, and that's what it's for.