An auditory Easter Egg.
This is usually a line of dialogue, frequently humorous but occasionally providing extra insight into a character or situation, that is difficult to notice. Often it's said quietly while something else is being shown onscreen, making the bonus very difficult to notice the first time until you watch with subtitles enabled. Once you know it's there, however, it's very easy to pick up the next time. A subtrope of Rewatch Bonus. See Freeze-Frame Bonus for this trope's visual counterpart.
Examples:Film - Animated
- In WALL•E, when the captain is going through the Axiom's status reports, the items checked include "jacuzzi pH balance" and "laundry service volume." Apparently with the same priority as stuff like the reactor core temperature!
- In Guardians of the Galaxy Vol. 2, when Rocket is playing Glenn Campbell's "Southern Nights," he comments, "I love this song." Listen for it just as one of the Ravagers steps on the trigger for his dart trap.
- Many pop songs have a variation of this, where with certain lyrics are very difficult to understand what is being said. Once one reads them in print, he or she can usually hear the words more clearly after that.
- Inverted in Portal 2, where Glados' ending song includes a line (addressed at Chell): "Maybe when I delete you, I'll stop feeling so bad..." She sings the second half of the sentence rather audibly, but the subtitles skip it as "unintelligible".
Hello, Unknown Troper. You'll need to get known to lend a hand here.