Well thats the way the ''r'' sounds in portuguese, so rato sounds slightly like ''jatu''. Now try saying "carro" "churrasco" :)
If any of you happen to speak Arabic, or helps me to imagine Portuguese r's as kind of a softer غ. Makes pronunciation easier.
I don't think the 'r' sounds that much like 'h', there are just two ways to realise the letter 'r'. You can either pronounce it rather at the front of your mouth or at the back. In Spanish (also in English), you pronounce it at the front, and in Portuguese at the back, just like in French. In German, we have both 'r's by the way ;)
Portuguese, like Spanish, distinguishes between two different R sounds, but the sound of the initial or double R in Portuguese varies greatly by region.