Congratulations on your new BP and a successful first feeding. One thing you can do to determine the best size prey for your snake is to get a digital scale that measures in grams and weigh your snake. The prey should weigh 10%-15% of the snakes weight. For example: If your snake weighs 100 grams then the prey should be between 10-15 grams. I keep track of my snakes weights and make a list of the rat sizes I need, then I take my scale to the pet store and root around in their freezer until I have all of the sizes I need. You can get digital scales from several places. You can order them online from places like ReptileBasics.com or check sites like E-Bay and Amazon for digital postal scales. You can also get a digital food scale from stores like Wal-Mart or Target in the Kitchen section. Hope this helps some...