The movie is called
Nightmares (1983), and the segment you are referring to is the 4th segment, called "Night of the Rat".
Originally made for TV, they were deemed too bold for the TV screen and so bundled together as a movie with 4 stories in one.
You can check the movie here -
http://www.imdb.com/title/tt0086014/
and if you want the DVD or VHS, its available here -
http://www.amazon.com/Nightmares-Cri...6912365&sr=8-1
Happy viewing.