Mystery #2Tier 2hormones / sleep
Why do you start to feel sleepy soon after it gets dark?
The sun goes down, the room dims, and before long your eyelids feel heavy. It happens even when you're not especially tired, and even earlier in winter when night comes sooner. Something about the dark seems to whisper 'time for bed'. How does your body know that darkness means sleep?
Your guess
What's your guess about how your body knows that darkness means it's time to sleep?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
Make a guess to unlock the hints and the answer.