What is a "pet pricing project?" Is it collecting prices at a pet supply store, or getting prices for animals?
One trick to use in certain kinds of stores (long shelves with not many employees in the aisles) is to take a cell phone photo of the product and the price posted underneath. That label contains the upc.
If you have a lot of prices to collect (I do lots of these; right now I am working on a 125 item international cost of living survey that pays $125 to get 4 prices each for the items.) is also good to use a hidden voice recorder (to look like you are listening to an iPod) with mic'd earpiece, like my iPhone has, and you can unobtrusively walk around looking spacey and "singing" while really mumbling prices/upc's to yourself.
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~Gilbert K. Chesterton