Well first in the theme song at the end if play it reversed
u can hear a small voice that says "three letters back" and if u play it fowards u can hear it says "switch a to z"
Another mystery is that at the end of the theme song it has a picture thats on the bottom it has a scrambled message like it says in the theme song u have to ilipat 3 letters back to crack the code and when ur done it says "stab is not what he seems"
Another mystery is that at the end of each episode in the credits it ipakita a scrambled message like the one to the right to decode it u have to us the term three letters back in the first episode it sinabi welcome to gravity falls well thats all for now if u want to u could leave tanong or comments