A typical yoga class involves deep breathing and moments of quietness and tranquility.

Yet that's not necessarily the case with laughing yoga - a popular practice in the US.

The technique, developed in India in the 1990s, involves laughing with yogic breathing exercises: chanting "ha ha ha, hee hee hee", for example.

It's based on the principle that you can laugh whenever you feel like it, and not just because you find something funny.

Laughing is said to have many health benefits, such as improving respiratory function and increasing the production of stress-busting endorphins. It's also believed to reduce the risk of heart disease, stroke and allergies.