I mean it was pretty obvious with their eyes darting then several lines of code appearing in the code editor.

Of course, this doesn't mean I've discovered 100% of the cheaters, just the obvious ones.

> Also, I'm curious: do you think having them discuss their solution in depth would have been a good countermeasure?

To some degree. But not everyone communicates as well as they code or vice versa, and then it comes to what you're trying to qualify.