Cartman comes home after their first day on the force, only to find Butters is still trying to give a semen sample in his bathroom. He tells him to keep trying. At the end, Butters finally comes downstairs with his semen sample, explaining he was trying the whole time and finally got it. However, right after Cartman tells him to keep trying, we see all the kids in class, and Butters is in his seat.
The kids earn a dollar (their first since starting their business) and hold it up. Then we see a shot of a picture frame with what's supposed to be the same dollar, but the serial numbers are different.
(At 1:04) There is no fence on either side of the old couple's home, but when the boys go in their backyard moments later, there is a fence on both sides of it.