What makes a COVID superspreader?

We've all heard that COVID spreads in clusters and sometimes the cluster comes from a single person who can infect nearly everyone around them.

They're superspreaders and it's been opaque how much virus a superspreader is actually responsible for spreading around.

Now a study has found that in a group of deliberately infected people, just two of them were responsible for nearly 90 percent of all the virus emitted - even though they only had mild symptoms.