The traits of Sodom. And other ways that eruvin may or may not take hold, but aren't really in the spirit of eruvin: one who doesn't allow others to eat from the eruv he has set aside. Or one who divides the content of the eruv. Both flout the essence of eruv, which is to bring people together, joining, sharing, into a unity. The Gemara also fleshes out why we need both of these cases. Also: Does the essence of eruv work because of the collective kinyan (formal act of acquisition) or because of residence taking hold? The owners of the house where the eruv is located don't have to contribute food themselves - either hosting counts as his contribution, or the others establish their residence in that home, as it were, via their eruv contributions. But then why do we make eruvin out of food and not money? Often enough, people don't have cash on hand on Friday afternoon. Also, the nature of the participation changes, based on those food contributions. What's the difference in the approach? One practical difference is how much the food itself has to be worth... Likewise, the involvement of a child. The approaches to eruvin on this daf undermine the mindset that eruv is entirely a loophole, and establish the value of eruv for community.