Break Into Meaning

(transitive) To begin suddenly.

Example:   Somebody broke into his car and stole his tools and CDs.
  I finally broke into the second package of cookies.
  He hopes to break into show business.
  The horse broke into a gallop as they neared the barn.
1945, George Orwell, Animal Farm, chapter 6
  Then, as usual, the sheep broke into "Four legs good, two legs bad!" and the momentary awkwardness was smoothed over.