"The mountain passes fill in with snow. The Taliban and the terrorists and the Haqqani and the Quetta Shura come over from Pakistan to fight our men and women. When it fills in with snow, they can't do it. That's what we call fighting seasons. In the warm months, fighting gets really high. In the winter, it goes down," explained Ryan.
"And so when Adm. Mullen and Gen. Petraeus came to Congress and said, if you pull these people out before the fighting season ends, it puts people more at risk. That's the problem."
"I think Ryan proved himself unexpectedly competent on foreign policy," said Republican strategist and CNN contributor Alex Castellanos, who worked for Romney's 2008 presidential bid. "I think Ryan met his test tonight. Ryan looked very reasonable."
As expected, the Obama campaign disagreed.
"I think Congressman Ryan was out of his depth and showed clearly the ticket is not ready for prime time on foreign policy, and I think that was a decisive difference between the two sides," said Obama campaign manager Jim Messina.
So what do debate watchers think? Did Ryan pass the competency test?
Six out of 10 debate watchers in the CNN/ORC poll conducted said that Ryan is qualified to be president.
5. Malarkey moves numbers
"Malarkey" is one of Biden's favorite Biden-isms.
He's been saying it for decades, but not usually with the kind of gusto he showed on Thursday before millions of prime time television viewers.
Soon after the debate began, when Ryan criticized the Obama administration's foreign policy, Biden fired back: "With all due respect, that's a bunch of malarkey."
What does malarkey mean?
People apparently rushed to their computers to find out. "Malarkey," it turns out, was the third-most-searched debate-related term of the night on Google. It was also trending on Twitter for a good chunk of time.
For the record: it's basically the Irish-American term for "nonsense."
According to Google, the other top searches during the debate were "Biden," "conflating," "Who is winning the debate" and "How old is Paul Ryan."