Meaning: Use your brain, dummy
While you might think that noodles don鈥檛 really look like heads, they do kinda look like brains. Originally 鈥渦sing your noodle鈥 was an insult 鈥 comparing a simpleton wagging his head around while thinking with a wet, floppy noodle. Nowadays, it鈥檚 no longer an insult and simply means "think about it."