That's horrible to hear, De-Ting. Sorry to hear you had to see your pet gerbil like that. I have two stories too, similar to yours, both involve dogs.
When I was eight years old, I was walking through the neighborhood to my friend's house. There was one house where the front gates were left open, and out of nowhere this massive dog ran out, stopped right in front of me, growling and barking. I was on the other side of the street, so it sprinted right up to me.
I thought it was gonna hurt me, or worse, but then this guy on his bicycle threw something at the dog, called out to it, then the dog ran after him and he rode away on his bike. I then ran to my friend's house. I never walked to my friend's house ever again, I always got lifts from either my folks, or his.
The next scariest experience was with my own dog, when I was ten. Our dog was old, about fifteen years old and he wasn't doing so well. I came home from school one day to find our dog laying on the concrete, and ants were all over his stomach, biting at him, surrounding him. I got so upset, I was crying and I was trying to get the ants away from him. Once the ants were gone, I sat with him for about an hour, sobbing, waiting for my parents to come home from work. My mum came home and well, the next day my parents took our dog to the vet and sadly he had to be put down.