The verb in this sentence is "peered." It describes the action of the scary face looking out from the window.
The man was frightened to see that his son had killed himself!
She had never been so frightened before.Mummy, James frightened me again.
Frightened is only capitalised if it begins a sentence, or is part of a title.
I was so frightened in the haunted house, it really scared me.
He was frightened badly. So I talked him down.
Macabre movies make me frightened.
Horses (and most other herd animals like cows and sheep) are frightened of almost anything they cannot recognize. Flapping cloth or paper can scare a horse away, as can an object or person that they do not know. They can be frightened by sudden noise or movement also.
The lion that looked like a beast frightened me.
The bird was frightened away by the noise. Are you frightened by swarms of bees? (One swarm can ruin your whole Saturday night!) A spooky carnival ride is one place where people enjoy being frightened.
That sentence doesn't contain a direct object.
A ghostly apparition frightened Scooby Doo.