盘腿坐在桌子上，他认真地思考晚餐吃什么好。
他认真的思考晚上吃什么好，当盘腿坐在桌子上。
He earnest thinks about what to eat when he puts his leg on table.

英式中文：（当他）坐在桌子上盘着腿，他思考认真地他晚餐应该吃什么。
参考英文：When he sat on the table with his legs crossed, he thought seriously what he should eat for supper.
语法解析：when引导的是状语从句，从句的主语和主句的主语一样，因此可以简化，when he sat on the table简化得sitting on the table，简化方法看《英语框架》95页。with his legs crossed也可以用crossing his legs互换，想一想，为什么一个用被动，一个用主动。what he should eat也可以简化成what to eat。