cracked open

[NewHope]

What does "crack open" mean?

I could not believe their heads have been beaten to open so that their brains flowed out.

Context:

"The police beat us," a 2002 victim told Voice of the Martyrs. "Some had their heads cracked open, some had their teeth broken, and some could not walk again because their arms and legs were so injured."

[Tdol]

It means cut so that they bled quite badly.