memory like a sieve; in one ear and out the other
Idiomatic expression for someone who quickly forgets what they hear; often used self-deprecatingly or to tease.
He has a memory like a sieve and forgets what you tell him right away.
I have a memory like a sieve, so could you say that again?
Standard kanji-kana mixed spelling; ざる is often written in kana for this idiom.
Full kanji spelling using the character for 'sieve'; less common and may not be recognized by all readers.
Compound of ざる (sieve) and 耳 (ear), literally 'sieve ear'. The image is of information leaking out of the ear like water through a sieve.