It is a phrase that means “to take something with a grain of salt“.
It is used to describe situations in which you don’t completely believe something that you are told because you think it is exaggerated or it is unlikely to be true. You can use “話半分“ for short.
Ken and Leo are talking about Tom.
- Ken: I can’t believe it; Tom said that he can speak seven languages including Japanese.
トムって、日本語を含めて7言語話せるんだって。本当かな!? - Leo: I think he probably means he knows some basic words in each language.
たぶん、各言語の基本的な言葉を知っているだけだろう。 - Ken: Could be. Actually if he was really good at Japanese, he would be in charge of Japanese projects.
そうかもね。確かに、本当に日本語が上手なら、日本のプロジェクトに配属されているよね。 - Leo: You should take what he says with a grain of salt.
(トムの言う事は)話半分に聞いておきなよ。
Meg is complaining about her boyfriend.
- Meg: I was supposed to go shopping with Tom yesterday, but our plans got cancelled because he caught a cold.
昨日トムと買い物に行く予定だったけど、彼が風邪をひいて中止になったの。 - Amy: I'm sorry to hear that. Is he getting better?
可愛そうに。よくなったの？ - Meg: Yeah, he is totally fine! Last night, I rushed to visit him only to find him playing video games. I mean he pretended to have a fever. He is such a jerk!
うん、ピンピン(orすごく元気)だよ！昨夜、彼の家に行ったら、ビデオゲームしていたの。熱があるふりをしたの。最低！ - Amy: Hahaha. Don’t take what he says too seriously next time.
ははは。話半分で(聞いた方がいいね)。