Comedian Craig Ferguson and Watchmen star Jeffrey Dean Morgan turned the air blue on TV on Thursday night after realizing they could curse without repercussions behind facial pollution masks.

The Late Late Show host Ferguson offered his guest a mask after Morgan revealed he was suffering from a bad cold, and when he joined the actor, the pair quickly figured their censored swear words could not even upset lip readers.

Morgan joked, "Holy s**t! Nobody knows what the f**k I'm saying," prompting an excited Ferguson to put his mask on and state, "We can cuss... Wow! What an awesome idea. I love you, man."

The rest of the pair's hilarious chat was largely bleeped as Ferguson and Morgan fell about like naughty schoolboys, holding the masks to their faces as they swore up a storm.