Alexis Denisof and David Boreanaz began getting the giggles as the program progressed. It got to the point that when Angel runs back into the Hyperion Hotel to report that there are hundreds of demons outside (he means the cars on the freeway), the two could not look at each other without dissolving into laughter. Take after take was wasting the time of the crew and other actors. They decided they would simply, then, not look at each other. But between 32 and 33 minutes into the program, they had quick glances, and the viewer can watch them trying to hold in the laughter.
When the spell is cast the first thing Cordelia says when she sees Angel is "Hello salty goodness!" Which is also the first thing she said the first time she ever saw him in Never Kill a Boy on the First Date (1997).
When Wesley is telling Gunn a bunch of lies about knowing what kind of demon Lorne is ("this breed is nocturnal and feeds on roots or possibly human effluvia..."), which leads them into a fight match, in the foreground, Fred approaches the tied-up, knocked-out Lorne and begins to pat at his forehead and hair, generally examining him. Amy Acker and Andy Hallett kept breaking into laughter, which meant that Alexis Denisof and J. August Richards had to keep filming their background fight again and again, take after take.
In television business jargon, an episode shot entirely on already-existing sets with a minimum of expensive extras like guest stars or extensive special effects (to keep the budget down) is called a "bottle show" or "bottle episode." The title of this episode, in addition to being a reference to its subject matter, is also a nod to the fact that the episode was deliberately conceived as a "bottle episode" to cut some of the price tag of season four.
It was Amy Acker's idea that Wesley should duct-tape Lorne to the pouffe, or hassock, in the middle of the room. Joss Whedon knew that he wanted Lorne to be in the middle of things, and Lorne had to be able to talk and interact, but he should not be able to move around or influence people except by reasoning with them. Whedon says in the Commentary that he had been baffled what to do with Lorne, until Acker had her suggestion.