'Late Night': Fallon Cracks Up During Sketch with 'SNL' Buddy Will Ferrell (VIDEO)

When Jimmy Fallon and Will Ferrell were fellow comedians on 'Saturday Night Live,' Fallon admitted that he couldn't keep a straight face around his co-star. Well, it was just like old times when 'The Other Guys' detective visited the host on 'Late Night' (weeknights, 12:37AM ET on NBC).

They "reminisced" about appearing together in a Canadian soap opera called "Jacob's Patience," and recalled that in one scene, Ferrell refused to use his arms.

"Yeah, I was doing a ton of freelance arm modeling back then. In fact, my arms were insured by Lloyds of London," Ferrell dead-panned.

At that point, Fallon just couldn't keep it together. They rolled the clip of their "scene" involving Ferrell's fake arms, and in it, Fallon's giggled continued.