I can't seem to get through their thick brains.
Get through someone means: to succeed in talking to someone on the phone, but what does "get through their brain" means? Is it an idiom derived from the idiom "get through someone"? I am a little confused on where the expression comes from, and what it means exactly. Could you explain what "get through someone" can mean, and then tell us what "get through their brains" mean?