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 Boob-Based Gag, 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 show that exploits this to appeal to an audience, 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).
Please do not add examples to work pages, this merely defines the term. Put applicable examples in the following tropes instead:
- Artistic Licence – Anatomy: Breasts moving in ways that are impossible in real life.
- Boob-Based Gag: The use of female breasts for comedy, rather than (or in addition to) Fanservice.
- Jiggle Physics: The simulation of the behavior of non-rigid objects and materials in a computer.
- Jiggle Show: Fanservice-based shows from The '70s that often involve jiggling breasts, particularly due to a lack of bras, and often also slow motion.