Found it myself. It's called the "startle" effect. Usually it's the typical "cat in the closet" scene, accompanied by a loud crash of percussion instruments in the movie score. Can be effective as you know, but it's waaaay overused and therefore becomes somewhat annoying in movies where the director should know better, and should not resort to cheap thrills.
Yes, the original "Cat People" (Val Lewton) had the first "bus effect" startle scene, but the term has morphed from a "bus" to "startle".
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Caliber .45. Works against zombies and most everything else.
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