開腦洞

to blow people's minds with highly imaginative, bizarre ideas

cave / hole / zero (unambiguous spoken form when spelling out numbers) / CL:個|个[ge4]

to open / to start / to turn on / to boil / to write out (a prescription, check, invoice etc) / to operate (a vehicle) / carat (gold) / abbr. for Kelvin, 開爾文|开尔文[Kai1 er3 wen2] / abbr. for 開本|开本[kai1 ben3], book format

brain / mind / head / essence