things that go bump in the night

Things that go bump in the night is the phrase which is used for any sort of scary and supernatural thing, being, monster or event that often occurring after the sun has gone down. Traditionally, most scary or frightening things happen at night so this phrase is speaking about that cliche in that things that go bump in the night are things which often scare people but are supernatural. For example, a ghost or vampire comes out at night but is imagined while a murderer would not be the same thing because they are not supernatural.