Suppose there’s a spot in a sentence where either of two synonyms would be effectively the same. That’s 1 bit of available entropy. Then a spot where either a period or a comma would both work; that’s another bit of entropy. If you compose a message and annotate it with 48 two-way branches like this, using a notation like spintax, then you can programmatically create 2^48 effectively-identical messages. Then if you check the hash of each, you have good odds of finding one which matches the 48-bit hash fragment.
Suppose there’s a spot in a sentence where either of two synonyms would be effectively the same. That’s 1 bit of available entropy. Then a spot where either a period or a comma would both work; that’s another bit of entropy. If you compose a message and annotate it with 48 two-way branches like this, using a notation like spintax, then you can programmatically create 2^48 effectively-identical messages. Then if you check the hash of each, you have good odds of finding one which matches the 48-bit hash fragment.