This study has been making the rounds, but it's worth noting here as well, since it documents how a single, infected person attending gatherings (funeral, birthday party) infected many others through close contact (e.g., hugging, sharing meals over the course of several hours), and how some of those then infected others.  Note the final bit of infection tracing reported:

Three symptomatic birthday party attendees with probable COVID-19 (patients A2.5, A2.6, and A2.7) attended church 6 days after developing their first symptoms (investigation day 17). Another church attendee (patient D3.1, a health care professional) developed confirmed COVID-19 following close contact with patients A2.5, A2.6, and A2.7, including direct conversations, sitting within one row for 90 minutes, and passing the offering plate.