To increase or expand suddenly, rapidly, or without control
To make or become greater or larger
As she straightened, his snowball was already in the air.
Again she lobbed a snowball at him, but in her haste she missed him by a wide margin.
I know it was selfish, but I felt emotions I never believed existed and I didn't want them to end… Things started to snowball from there.
"I wonder what happened to snowball," she mused.
I suppose Snowball would be a common name, and she's certainly an uncommon cat.