Earlier, I posted several reasons why the source was most likely the Wuhan Lab. Recently, this article came to my attention. It points out the smoking guns that make a lab accident the most likely source of the virus.
It's 11,000+ words and technical, but here are the key points.
1. The furin cleavage site. Viruses attach to human cells via something called a furin cleavage site. The furin cleavage site DOES NOT EXIST in any known SARS-related beta-coronaviruses. However, creating furin cleavage sites is relatively easy. Here's quote from the article (emphasis added.)
“Since 1992 the virology community has known that the one sure way to make a virus deadlier is to give it a furin cleavage site at the S1/S2 junction in the laboratory,” writes Steven Quay, a biotech entrepreneur interested in the origins of SARS2. “At least 11 gain-of-function experiments, adding a furin site to make a virus more infective, are published in the open literature, including [by] Dr. Zhengli Shi, head of coronavirus research at the Wuhan Institute of Virology.”
2. Double arginine CGG codons at the furin cleavage site. The explanation is technical, but single arginine CGG codons are rare, even though arginine codons are the preferred type of codon for human infectivity. Double arginine codons have never been seen to exist in any other coronavirus. Quoting from the article....
For the lab escape scenario, the double CGG codon is no surprise. The human-preferred codon is routinely used in labs. So anyone who wanted to insert a furin cleavage site into the virus’s genome would synthesize the PRRA-making sequence in the lab and would be likely to use CGG codons to do so.
Here's the article.
https://thebulletin.org/2021/05/the-origin-of-covid-did-people-or-nature-open-pandoras-box-at-wuhan/