'Big Little Lies' star Adam Scott was left embarrassed when ''a string'' of snot came out his nose in front of his co-star Reese Witherspoon after the actress told a joke.

The 46-year-old actor plays the 'Legally Blonde' star's character Madeline Mackenzie's husband Ed Mackenzie in the hit HBO drama series - which recently returned to screens for a second series - and has recalled the cringe-worthy moment on set.

Asked if he has ever felt intimated by the A-list cast, which also includes Nicole Kidman and newcomer Meryl Streep, Adam said: ''It's hard because everyone in the cast is so incredibly famous and talented, it's crazy ... One time with Reese Witherspoon and I were shooting a scene, it was the last scene we had together in season two and it was a scene in a therapists office. In between takes she said something funny. A string of snot, like, came out, and wrapped around my nose. And I just excused myself, went and found the make-up person, got a Kleenex and wiped off.''

Asked by host Conan O'Brien on his titular show if he has ever brought up snot-gate with the 43-year-old actress, he admitted: ''I thought, 'Should I reference what just happened to Reese? Should I make a joke about it or just apologise for the disgusting thing that just happened?' And I didn't.''

The 'Black Mass' star joked that he will wait till he's on his deathbed to remind her what happened.

He grinned: ''Let me tell you as a friend, that no, too much time has gone by now. The only thing you can do now is maybe on your death bed, summon Reese to your side and go, 'The snot! The snot! I'm sorry!' and then die and have that be the last words you ever spoke.''