How is the terror bird's attack method theorized to have functioned?

Answer

Using the massive bill like a gigantic hatchet or cleaver

Researchers believe the primary method of attack involved using this massive bill like a gigantic hatchet or cleaver to inflict severe, incapacitating wounds on larger animals.

How is the terror bird's attack method theorized to have functioned?
birdPredatoranimalextinctionpaleontology