拉肚子在英语中可以翻译为 "have diarrhea" 或者 "have a stomachache." 这个说法来源于拉肚子时肠道内的液体物质会使人拉肚子，从而导致腹部不适。

例句：

"I think I ate something bad and now I have diarrhea." (我想我吃了些坏东西，现在我拉肚子了。)

"I have a stomachache because I ate too much junk food." (我吃了太多垃圾食品，现在我拉肚子了。)