Little bit off topic, but the entire argument about Africans being completely unaware of the European style of slavery sounds like complete and total bullshyt.
Africans were not morons, they understood that they differed drastically from the Europeans in terms of language, dress, technology, and customs. And all of this can be proven by recorded accounts. Yet i'm suppose to believe when it came to slavery Africans just assumed Europeans practiced it the exact same way they did, despite Africans understanding that the Europeans differed from them on every other category imaginable? Sorry, that doesn't even sound plausible.
Now, I'm not saying they were fully aware of the cruelty associated with cattle slavery in places like Brazil, but I seriously doubt that they assumed the European style of slavery was equivalent to theirs. Matter of fact, the African traders who made the exchanges at the coast could probably tell by the way Europeans handled the slaves that their concept of slavery was completely different from anything they knew.