What is Swarming?
Swarming is the whole team (or most of it) converging on one work item to finish it before starting anything else — the logical extreme of "stop starting, start finishing." Triggered by blockers, aging WIP, or sprint-goal risk, it trades individual efficiency for flow: items finish dramatically faster even though some hands are "suboptimally" used.
Its scheduled cousin is mob programming; its cultural prerequisite is a team that measures itself by finished work, not busy people.
Worked example
Wednesday: the sprint's key story — payment reconciliation — is stuck, and its developer is grinding alone. The team swarms: one pairs on the core logic, the tester builds edge-case data, a third untangles the environment issue blocking deployment. Done by Friday morning. Individually, three people were "inefficient" for two days; collectively, the sprint goal survived — the only metric that was ever real.