Episodes with "extra Joe" happen randomly, with little to no warning. He will ask oddly specific questions, or outright struggle to ask one at all. He will also make jokes and puns considered lame by Lars. The former will often call him out for this and apologize to the guest, if there is one. Sometimes the guest will play along nicely, while other times they will engage in the roasting alongside Lars.
Lars and Joe have both agreed that the former is a stronger question asker, and so in later episodes they have shifted the balance toward Lars asking the questions and Joe adding color commentary.