Problem
Scenario: You have agreed to take care of your friend's dog; Buddy, while she goes on a trip to Antarctica. On your two-hour trip to take your friend to the airport you get so caught up talking about her upcoming adventure that you do not have any time to ask questions about her new dog (Buddy) who is riding in the backseat. After you drop your friend off, just in time to catch her flight, you drive the two hours back home and realize that your friend accidently took the dog's bag with when she ran into the airport. You realize that you do not have access to your friend's house and cannot contact her. It is a new dog so there is no one else you can contact that knows its normal routine. You stop at the local pet store and ask the salesperson to help you pick out food and supplies to take care of Buddy for the next few weeks. They send you home with a bag of salmon and potato dry dog food, a few toys, and a dog bed. When you get home, you put some of the dog food in a plastic bowl that you had been using to store oranges and lemons. You offer this to Buddy, but he refuses to eat his dinner. This puts you in a little bit of a panic since your friend is on a long flight and will then be on a ship to Antarctica so contacting her will be difficult. You take a deep breath and decide that you can try to solve this problem on your own.
What are three things that you should keep constant (the same) during your experiment so that they don't influence the outcome of your experiment?