the word for brain here is cerebrum, and it’s been literally split in two
I’ve seen wordplay like this before in Latin, but with compound words that are clearly made up of separate parts
but “cere” is not a word and neither is “brum”
you could translate it something like
“he split his br apart ain with a rock”
and it’s only slightly less unreadable than that due to freer word order
needless to say something I’d expect more from a modern experimental poem than an ancient epic
okay not a Latinist but a Latinist’s wife as well as Egyptologist-writer with an undying love for wordplay, but can I suggest the following translation:
“he split his br in two ain with a rock”
this for the additional vocalised puns where when you say it out loud, ‘br in’ sounds like “brain” and ‘two ain’ sounds like “twain”.