The motion displayed is often asynchronous — each breast is animated separately and possesses its own individual movement. Their mass and elasticity may be so ridiculous that they defy physics by Rule of Sexy, lurching and heaving in ways that are unrealistic or outright impossible.
Closely related to Gag Boobs, as this may happen by Rule of Funny as well as Rule of Sexy. If the animation is exaggerated or silly, it may be accentuated by Stock Sound Effects to make it seems like a character's bouncing boobs are made of rubber or propelled by springs.
Also known as Gainax Bounce or the Gainax Bounce Effect. The term was coined by fans some time before 1993 and makes reference to the anime production of Studio Gainax, many of whose earlier releases made use of this particular variety of Fanservice. According to a Usenet post from 1993, one particular busty young woman from the Gainax anime Otaku no Video inspired a tongue-in-cheek unit of measurement for Gainaxing: one full bounce is apparently equal to one "Misty May".
In Real Life, a woman's breasts can bounce or jostle, usually as a result of physical activity and especially if they are large. However, this experience can be inconvenient, uncomfortable, or even painful. Compare D-Cup Distress when the Surprisingly Realistic Outcome of this awkwardness is acknowledged.
A Pec Flex is a variant of this done by a muscular male character. For a live-action TV series that exploits this, see Jiggle Show. For real-time generation of jiggling movement in video games, see Jiggle Physics.
Do not confuse this with a Gainax Ending (where it's the individual parts of the viewer's brain that gets contorted in different directions).
- An advertisement for sports bras consisted of women on a court bouncing balls along with certain parts of their bodies. In Slow Motion.
- Aachi and Ssipak has a female character that does this throughout the movie to hilarious effect. At one point, she somehow manages to find herself strapped to a motorcycle, riding on her rack, while bouncing down some stairs.
- Dinocore has Kaya, who is clearly designed for Parent Service, given that the show is a kid's show with a busty action girl with bouncing breasts. Only in season 1, though.
- Ralph Bakshi's Fire & Ice features a very early (1983) pair of life-drawn (but hugely amplified) bouncing breasts on Princess Teegra.
- The Little Mermaid (1989): Averted. While mermaids are shown to wear nothing but bikini tops, they use ones made from seashell cups. Because seashells are hard and rigid than cloths, they prevent their chests from bouncing, even underwater.
- When Evil Calls: Michael ogles the female basketball players while they practice, with their breasts bouncing. Then after he makes his wish he sees them bouncing nude as well.
- Jessica Rabbit from Who Framed Roger Rabbit. Her breasts were purposely drawn to bounce in the opposite rhythm of a normal female's chest while walking; she bounces down when a real person would bounce up, and vice versa. They go "boing"!
- The Suicide Squad. Camila—President Luna and later Suarez's Sexy Secretary—is seen for only like a total of 5 seconds, but even in that miniscule amount of screen time, we can see that her defining characteristics are her massive tits that bounce all over the place.
- Yvette, the French Maid from Clue, has a dress cut so low that her ample bosom bounces with every breath. In her opening scene, she sniffs the air and her breasts appear to be inflating as a result.
- Crazy Ex-Girlfriend has an entire song about this called "Heavy Boobs". Namely, how doing this hurts like hell. By the end of the song, all the dancers are wincing and clutching their chests tenderly.
- Dark Matter: Five's season 2 wardrobe doesn't appear to include a proper bra, a fact that is most obvious during her running scenes in "I've Seen the Other Side of You".
- Killing Eve: Villanelle has this happen as she's chasing Konstantin.
- The Wilds: Nora displays this while running with Quinn in a flashback, apparently not having a bra on at the time.
- The Caramella Girls in the official Caramelldansen music video, though it can be hard to spot due to the screen also bouncing.
- "Turn Down For What" features this trope taken to an extreme, where a middle-aged woman's Gag Boobs move (independently!) in time with the song's beat.
- Ootsuka Ai's "Pon Pon" has a fan-made video floating around that ratchets this trope Up to Eleven. Imagine hundreds of bouncing, jiggling, animated breasts from every anime ever, all edited in rapid-fire sequence and in perfect time with an equally bouncy, infectious J-Pop song that youll never get out of your head. The whole effect is simply glorious.
- In Baywatch, the Match Sequence has the camera pan down a line of female Baywatch lifeguards wearing sexy swimsuits. An operator configuration enables jiggling breasts.
- Downplayed in Aerosmith. "Walk This Way" begins with a shot of three girls at an Aerosmith concert, all with noticeably jiggly breasts - but they're shown from behind, obfuscating their movement.
- In the "Growing Pains" animation produced for NEMO Science Museum's "Teen Facts" exhibit, while the narrator describes the final developments of male puberty (such as ejaculation and body hair), the girl becomes interested in how her own body had developed, clearly enjoying swaying her hips and making her breasts bounce. Especially making her breasts bounce.
- On Shut Up! Cartoons we have a few examples:
- Oishi from Oishi Highschool Battle is gainaxing all the time. Oishi breasts are actually prehensile, on occasion the reach out and smack people, or fire laser beams from her nipples.
- A sequence in Samurai Daycare opening is a close-up of asymmetrical breast-jiggle.
- Appears to have been attempted in Acedemy Sugoi Seiun when Sakura is running to school, but due to the animation being only 2 frames it's hard to tell.
- Emerald is subject to this in RWBY, even more so than Yang thanks to having a gigantic cleavage window. Her model was specifically designed so her chest moved asynchronously, leading to the animators having to tone it down at times. After Season 3, however, the change in the animation engine used (as well as the death of Monty Oum) have put an end to this, and no breast jiggle has been seen in the series since.
- In a Wonder Woman parody strip, she and Superman are fending off some bad guys shooting at them. Superman stands in his trademark pose while the bullets bounce off of him, and he asks Diana why she blocks with her bracelets if she's invulnerable like he is. She stops blocking and lets the bullets hit her; they bounce harmlessly off her chest...but her breasts bounce back at every hit. The bad guys catch on and they all start shooting at her breasts to enjoy the show. She simply looks at Supes with an "I rest my case" expression. He concedes her point and she goes back to blocking.
- In C Karrus, Juline's breasts seem to do this with every movement, partially contributing to her constant wardrobe malfunctions.
- In GunKitty the character Yumi Bloom's breasts jiggle in almost every other panel.
- Mrs. Beady from Barnyard and Back at the Barnyard has her boobs jiggle, even when she gets up from the chair. A case of this being used for Fan Disservice, considering she's quite ugly.
- Manuela from the Les Lascars, even when she does the smallest movement like turning her head, her boobs move.
- In the American Dad! episode "Helping Handis", Steve ends up growing a pair of boobs as a result of an experimental steroid given to him by his dad. Steve's newly developed breasts jiggle quite a lot throughout the episode.
- The aptly named Big Boob June from The Cleveland Show, whose breasts jiggle with nearly every movement she makes.
- One Family Guy episode has Lois' boobs swelling up as a result of breastfeeding Stewie while he was teething. Peter, in an attempt to get Quagmire to realize that he's making a mistake by getting married, purposely shakes Lois which jiggles her boobs.
- Vanessa Warfield's breasts can be seen jiggling as she runs in the M.A.S.K. episode "Riddle of the Raven Master".
- In the Teen Titans episode "Date with Destiny", Starfire's chest briefly bounces while she vehemently refuses to agree to the demand that Robin takes Kitten to the prom. Naturally, Robin doesn't want to either, but they have little choice, or else Jump City would be overrun with Killer Moth's mutated swarm of moths.