To happen to hear; to overhear (something informally, often as hearsay rather than from an official source).
電車の中で隣の人の会話を小耳に挟んだ。
I overheard the person next to me on the train.
仕事の件を小耳に挟んだら、まず上司に確認するべきだ。
If you hear something about work, you should check with your boss first.
試験の結果について小耳に挟んだが、正式な発表はまだだ。
I heard something about the exam results, but there hasn't been an official announcement yet.
小耳に挟んだ話を鵜呑みにしないほうがいい。
It's best not to take hearsay at face value.