Sloshy, frothy, soft whipped cream, firm whipped cream, coarse whipped cream.
Then, suddenly, the cream will seize, its smooth shape will collapse, and the whirring will change to sloshing.
The butter is now fine grained bits of butter in buttermilk, and a few seconds later, a glob of yellowish butter will separate from milky buttermilk. Drain the buttermilk.