In this new Gothamist interview to promote Daniel Tosh's gig Saturday at Town Hall, Tosh acknowledges that he froze mid-joke during his set last week on The Tonight Show with Jay Leno.

What happened? I forgot my material. But it was the worst time during my set too, because it was my last joke. So I was in the middle of it, and it was fine, and I just froze. And I just kept talking. You could tell I had no idea what I was saying, and thankfully they chopped like twenty seconds of me panicking out of the show.
Did Jay say anything? Yeah, he came up to me and said “Hey, what happened?” And I just said “I don't know.” It was kinda weird, my timing was thrown off because people were clapping at a joke that I had never heard people clap at before. So I was thinking “why are they clapping here?” and before I know it my mind is just wandering. But they fixed it and everybody was none the wiser, unless you know the bit. But he couldn't have been nicer about it, and I've done the show many many times, so I'm not panicked that they're not going to have me back.

You can watch his performance from March 12's show temporarily on Hulu (they only keep three week's worth of full episodes online), and see how they edited Daniel Tosh's set. I don't know that I would have noticed if Tosh hadn't said anything. Also, I have noticed that Leno's and Letterman's crowds seem to have been even more appreciative of stand-up comedians recently, and the multiple applause breaks from a hot crowd can sometimes get your mind off its game plan when all you're thinking about is executing the four-five minutes. So it's nice to see that the producers and Leno care enough to make sure the comedian comes off looking his/her best.