chew the cud upon sth;rack (/beat/crack/cudgel/ransack) one’s brains;think one’s head off; work one’s head to the bone
? 他在～考慮一條妥善的道路，使自己安全的出去，又安全的回來。(梁斌《紅旗譜》) 422) He racked his brains for a safe way by which to slip out and return。
絞盡腦汁jiǎo jìn nǎo zhī
絞：擠壓。比喻費(fèi)盡心機(jī)，想盡辦法。rack one’s brains, puzzle one’s brains out, beat one’s brains, cudgel one’s brains, drag one’s brains