A proverbial expression admonishing someone not to lie down immediately after eating; not literal — a warning that it’s unhealthy or rude and may lead to weight gain.
子どもに『食べてすぐ寝ると牛になるよ』と言って、寝る前に散歩に連れ出した。
I told the child, 'If you lie down right after eating, you'll become a cow,' and took them for a walk before bed.
おばあちゃんは昔から『食べて直ぐ寝ると牛になる』と言って、いつも注意してくれる。
My grandmother has always warned me, 'If you lie down immediately after eating, you'll become a cow.'
冗談めかして『そんなに食べてすぐ寝ると牛になるよ』と言ったら、みんなで笑った。
I jokingly said, 'If you eat that much and sleep right away you'll become a cow,' and everyone laughed.