The actor took time out from his busy TV schedule to film a cameo on the beloved U.S. education show, on which he was given the task of defining the word soggy.
In a clip, obtained by Entertainment Weekly, the funnyman teams up with lamb owner puppet Murray to search the house for a wet object - but to no avail.
However, the pair finally succeed when Murray hauls out an elephant, which showers Krasinski with water from his trunk - leaving the It's Complicated star soaked and "soggy".
The episode is set to air in America next Thursday (29Dec11).
Krasinski follows in the footsteps of Katy Perry and Emma Stone, who have also recently guest-starred on the programme.