How To Convince My Mom To Let Me Get A Rat?

I Already have A Dwarf hamster To Show Her That I Can Take Care Of A Rodent.My Mom Is Totally Afraid Of Rats.She Thinks They're All Just Unclean,Nasty Little Things With Rabies And Parasites.She Also Think Guinea Pigs are Just Fluffy Rats.She Even Said That She Would Let Me Get A Snake Before She Would Let Me Get A Rat.I Don't Want A Snake!How Do I Change Her View On Rats So I can Get One?