The 37-year-old 'Sherlock' actor stopped by the show to help the muppets solve a math problem, reported Ace Showbiz.
In the video titled 'Benedict Cumberbatch and the Sign of Four (or is it Three?)', Murray Monster declares himself Murray-arity, a reference to 'Sherlock' villain Moriarty.
He asks the British actor to solve a 'brain-bending challenge', which is to determine whether there are more apples or more oranges on the table.
The third season of Cumberbatch's 'Sherlock' just wrapped up its run in the US last Sunday, February 2 on PBS. The actor was recently also seen in movies '12 Years a Slave' and 'The Fifth Estate', and lent his voice to the dragon Smaug in 'The Hobbit: The Desolation of Smaug'.