On a more informative note: I used to be a computer programmer. As I was also manager of quality I was in the habit of assigning a second programmer (not associated with the given project) to do joint walk-throughs with the app's programmer/team at key milestones. Particularly with single-programmer jobs this could be difficult as - back then anyway - there's a lot of creative scope and variation in how programmers code. It's not always easy to understand someone else's design approach and decisions.
In other words, sometimes having someone else check properly looked like it could take so long they would've coded it faster themselves.
I imagine things have become much more systematic and standardized these days.
Nope, sorry, most of the industry's still in the same state :)
I'm a programmer as well.