Confusing similar words in Spanish

Here are a few words that I get confused with sometimes as they are similar... feel free to post any other words you find confusing and what the difference is underneath this to start to create a useful list

Pero - but
Perro - dog

Sí - yes
Si - if

Casado - married
Cansado - tired

Re : Confusing similar words in Spanish

They are very confusing, i agree, i'm taking spanish for my highers later on but at the moment i have to get stuck with french.
Even though these words on their own are confusing, when put in a sentence they make total sense, dont you agree?