While shopping for new mouse cages today at Petsmart, my SO and I decided to look for a high-protein and -fat diet that we could use to supplement our lactating mouse's diet (we've just been giving her cheese and sunflower seeds in addition to her regular lab blocks). Most of the packages contained enough food for a few thousand mice (and many had scarily vague "animal fat" listed as an ingredient), but we eventually found a one-pound sample pack of "large breed puppy" food that was only $1.50.
Upon checking out, the perky cashier asked, "So, what kind of dog do you have?" After explaining what I was doing (being geeky and talking about fat and protein contents), all I got was an "Oh, interesting."
We were impressed that Petsmart only stocks one sex of small animals at each store, so people can't buy mixed-gender pairs (or accidentally get pregnant animals that were kept in mixed company). This seems like it should help novice small-animal owners from getting themselves in over their heads.