Compared to Rattata, Raticate is far more of a predator, and the majority of its features are adapted for this purpose. Its most notable feature are its large teeth; like most rodents, Raticate's teeth grow continuously throughout its life, and must be constantly worn down by gnawing. It is also known that Raticate's fangs are tough enough to break concrete. It has long whiskers and a long tail. Raticate looks like a rat, just like Rattata. Raticate tends to stand on its hind legs, as opposed to its pre-evolution.
Raticate's webbed feet allow it to swim well when it hunts.
Raticate is the evolved form of Rattata as of level 20.
It seems to be based on the nutria, or coypu. Whilst Raticate's name comes from rat and eradicate.
It is mentioned in several Pokédex entries that Raticate swims for prey, however, it can not learn Surf.
There once was an overlook in the anime where Rattata was standing next to Raticate. Raticate was actually as small as Rattata, which shouldn't normally happen considering Raticate are larger.
There is a popular theory that claims that in the original Japanese Red/Green games, the Raticate that your Rival used in battles before Lavender Town died, due to your Rival's lines, the fact you meet him outside of the Pokémon cemetery and the fact that his Raticate doesn't make any other appearances over the course of game.