Biden, who is Catholic, responded by crossing himself, and saying in jest, "Bless me, Father, for I'm about to sin."
Biden continued of the debate, "I've never seen anything quite like that. I haven't."
Fallon asked Biden, "Have you ever seen that [much] fact-checking? It seemed like fact-checking was a big thing."
Biden shot back, "I'll tell you what. I've never seen anybody who knew as few facts ... It's not a joke ... It's like whoa."
Added Biden: "You know what surprised me? I'll be serious for just a second. What amazes me about Donald Trump -- and he's probably a decent guy -- is his lack of sensibilities ... I mean, the way he talks ... 'I paid no taxes, that makes me smart.' What does that make us? Suckers?"
A puzzled Biden continued, "Can you think of a president ... who would say anything like that. Name one. It angers me quite frankly. The American people don't like being played for suckers."