Some pretty high-profile crimes have been solved by examining how the perpetrators, or accused innocents, use language. The way a person uses words, grammar, and puctuation creates a personal style and vocabulary that's somewhat like a fingerprint. Linguists know how individual these styles can be, and forensic linguists detect these patterns as clues to uncovering the truth in crimes.
When I listened to this video, I was deeply impressed by what forensic linguists can do, but I could also see how we all can learn these skills with time and effort. I'm no linguist, but having dealt with the written word for so long (and the spoken word before that), I know my own writing habits and try to correct for their overuse, not always successfully. I also recognize the styles and habits of writers whose words I proofread and edit. Avid readers recognize the style of their favorite author even when the byline is different. And everyone knows when someone close to them is drunk when they are texting. Language is something we all learn as children, but the way we use it eventually gains its own personal stamp.
There's a science fiction story from the early 1960s where an energetic brilliant exotic immigrant man earns his place in the U.S. space service but is kept from high-profile missions. Somehow he replaces the astronaut meant to go to, I think, Pluto, and he gives away who he is in a radio interchange by his pronunciation of the number six. He says, "Nine, eight, seven, sikkis... The flight director grasps this, but too late to stop the launch. The rocket is away and the man gets his chance.