phrozendata: It does not smell like shit, and is not unpleasant. The smell is like rich soil, because that's basically what it is. Just be sure to collect manure that is dried up and a little bit old (but not too crumbly and dusty).

slowdiver: I prefer to mix my substrate with manure directly in trays, let them colonize, then case them. Some people, like realfunguy, like to "case" their substrate with a layer of manure (this is not a true casing, though, because the manure is digested by the mycelium, which would make it another substrate layer instead of a casing layer). If you were to colonize the manure in a plastic bag, you would have to break everything up in order to fit it into a tray.