Answer:
i have read so many peoples views of this song,some say it represents America,losing its way,some say it is a love song,some say it is a friendship song,i believe sam beam wrote it the way he did so anyone could put a meaning to it but still holds his meaning.i think it is about suicide.a male/female,found their love,(have i found you)and lost it at the same time(or lost you)(flightless)meaning dead.idk what American mouth means.but at two points of the song he says "big pill loomng"meaning the thought of taking that people is in his mind because life with out his/her love isn't worth living.then "big pill,stuck going down" means he/she finally took it..the fat house cat pissing,could mean that when cats are close to dying they pee everywhere.now im a fat house cat could be translated into this.he/she in an older part of life,useless,with out his/her love,not doing anything but watch others be with their love,and he/she has no point in living and ready to die.hince the peeing everywhere,close to death.so he/she finally ends the pain with the pill that has been looming in his/her thoughts.i wish i could put a deeper meaning to it but i think the song itself is deep enough.i may be wrong about the interpretation.this is just what i think.