I have been told that I was (as a very sensitive child) scared of both The Count and the Yip Yip aliens from Sesame Street. But in terms of experiences I viscerally remember, at about 9 or 10 I snuck in the back of the room while my parents were watching Alien and saw THAT scene.
In honor of scary media month: what is the first piece of media you remember truly frightening you as a child?