I've seen these called "bosu balls" too, they must call them yoga balls in UK. What a plot, the man filled the ball with carbon monoxide in the trunk of the car, it slowly leaked and killed his wife and daughter!
Hong Kong yoga ball: Man found guilty of killing wife and daughter
19 September 2018
As the verdict was read out, Mr Khaw (centre) shook his head and one of his children burst into tears
An anaesthetist has been jailed for life for killing his wife and 16-year-old daughter using a yoga ball filled with carbon monoxide in Hong Kong.
Prosecutors said Khaw Kim-sun, a Malaysian national, left the inflatable ball in the boot of a car where the gas leaked out and killed them in 2015.
Police were initially baffled when they found the pair dead inside the vehicle.
...
There was a yoga ball in the boot of a locked car where Mr Khaw's wife and daughter were found dead
Read more at: https://www.bbc.com/news/world-asia-45573474
This sounds like a deserved death penalty case. I don't know if the laws in Hong Kong are different.
