Cheers guys.
My conclusion is that I didn't get across what I was aiming to convey. The jokes are purely incidental, and they are *deliberately* poor. This wasn't meant to be a vehicle for poor jokes!
The mood was supposed to be more like Barratt and Fielding's early zookeeper sketches; Seb is a self-conscious fool, and Carl is an arrogant fool. I just think the phrasing didn't fit that mood effectively. No matter. Thanks for the feedback.