Blowing repeatedly (e.g., to cool something down); the sound/action of puffing air to lower temperature.
熱いうどんをフーフーしながら食べた。
I ate the hot udon while blowing on it to cool it down.
スープをフーフーしてから飲んでください。
Please blow on the soup to cool it before drinking.
彼女は冷めるまでフーフーしていた。
She kept blowing on it until it cooled.
Huffing and puffing; breathing heavily or gasping (often used as ～言う).
彼は階段を上ってフーフー言っている。
He's huffing and puffing after coming up the stairs.
子どもたちは遊びすぎてフーフーしていた。
The kids were out of breath from playing too much.
Struggling (with work, studies, etc.); having difficulty and complaining or gasping about it (often used as ～言う).
試験勉強でフーフー言っているが、もう少しで終わるよ。
I'm struggling with exam study, but it'll be over soon.
彼は新しい仕事に取り組んでフーフー言っている。
He's having a hard time tackling the new job.