Space Hamster

The Space Hamster is a pet that you can purchase at Citadel Souvenirs. Once purchased it appears in the Captain's Cabin of the Normandy SR-2 beside the entrance to the bathroom opposite your personal terminal. When you select the cage, the Space Hamster will come to the glass, look at you, then scurry back into its box with an audible squeak.

Trivia

 * The Space Hamster is a reference to BioWare's Baldur's Gate II. A party member named Minsc carried a "miniature giant space hamster" named Boo in his inventory; any attempts to remove the rodent would result in an audiofile being played, the same "squeak" that the Space Hamster emits when interacted with.