New addition to my family

[Android-18]

http://www.ehow.com/how_2141591_tell-dif...e-rat.html

A rat is generally smarter than a mouse. For instance, if there is a new food source in their area of transit, they may force an older weaker rat to eat it and then watch to see if he dies or not in case the food is no good or contains poison. If that rat dies, they will urinate on it and avoid it. You have probably heard that you may only catch rats once on a snap trap and then you have to try something else. With mice this is not the case, they will come back to the same trap over and again.

One example. Just look up on google.