A mouse and a rat are not the same animal. A rat is larger than a mouse. They are both common rodents on all continents but not Antarctica. Other rodents are squirrels, porcupines, beavers, guinea pigs and hamsters. So if you see a little mouse, it will not be the same as a bigger rat, but will look similar.

A rat is any type of rodent. A mouse is a specific type. Meaning that all mouses are rats, but not all rats are mouses. Generally, the word rat has a negative connotation, because people think that mouses are cute, but rats are ugly.