Rats have poor vision, ruby or pink eyed rats will often sway its head from side to side to add "motion" to see better. Rats don't see in color.
Rats normally prefer to have cagemates.
It is possible to have a group of females, or males live together, though caution should be taken when introducing a new rat. While it's great to have both male and female rats, take caution in letting them play together. Rats can mate in about 2 seconds.
Generally speaking, males make better "lap" pets, preferring to sit and have their ears scratched by an attentive human friend. Female rats are very curious and love to explore and play games. Both genders make great companions.
Rats can eat other small pets. They are omnivores, and have enough predatory instinct left in them to consider birds, fish, and even other small rodents as "snacks".
The oils in cedar and pine are very toxic to rats and should not be used as their bedding. Aspen however is fine.
A rats temperature is regulated through its tail.
A group of rats is called a "mischeif".
Red discharge from a rats nose or eyes is usually porphyrin, not blood. Unlike blood, porphyrin is flourescent under UV light. It is produced in glands behind the rats eyes. Overproduction of this discharge can be caused by stress or illness.
A happy rat will chatter or grind its teeth. Often, chattering teeth results in "eye-boggling", caused by the lower jawbone pressing the backs of the eyes. This chattering is called "bruxing".
You cannot catch rabies from a rat. Rabies is produced in saliva, and rats have a "dry bite".
PEW stands for "Pink eye white", the fancy term for albino or any all white rat with pink eyes. Conversly, BEW stands for "Black eye white".
Rats can be trained to do simple tricks.