Split Brain

I won't spend too much time on this as it has been covered in detail elsewhere.

Oracle Technetwork

The Geek Diary - Split Brain

If you are using clustering, especially with problematic networking just be careful that nodes don't start acting independently of each other. Nodes taking over the others as though they have failed when in fact the problem is the interconnectivity. It is not something many DBAs will see and probably never will.

So if someone mention "split brain" don't worry it is not a monster movie, just an Oracle clustering problem.