Consider the following excerpt from the novel Lonesome Dove by Larry McMurtry:
“Well, it ain’t a holiday,” Call said. “Work to do. Me and Deets will go see if we can help them boys.”
“That Newt surprised me,” Jake said. “I had it in mind he was still a spud. Is Maggie still here?”
“Maggie’s been dead several years,” Augustus said. “You wasn’t hardly over the hill when it happened.”
“I swear,” Jake said. “You mean you’ve had little Newt for all these years?”
Here, I understand it as Jake being surprised and taken aback by what Augustus says. What I don't understand is his reply, "I swear". What does that mean in this context?
If anything, Augustus saying "I swear Maggie's been dead several years," would've been easier for me to understand