suck something in
phrasal verb with suck verb uk/sʌk/ us/sʌk/
收缩（腹部或面部肌肉，尤指为了显示身体较瘦）
to pull the muscles of your stomach or cheeks inwards, especially to try to make yourself appear thinner
I walked past them in my swimming costume, sucking my tummy in as hard as I could. 穿着泳装在他们身边走过时，我尽全力吸住肚子。