Oh one more thing - at one point maybe 2 months after getting these fish, the oscar started to nip at the ghost knife sometimes. It never did any damage to the main body of the knife, but I noticed a tear every once in a while on the ribbony lower fin that hangs off the ghost knife. The knife wouldnt even swim away, itd keep eating and basically act like it didnt even notice. But from then on, every time I saw the oscar swim at the ghost or nip at it, i would poke at the oscar with my water tong things - never actually touching it, but indicating back off the ghost and making it swim away. I did this for about three weeks, and now there is absolutely no hostility between the two, the tears healed really fast, and I havent seen any in months.
I swear the ghost will now taunt the oscar to try to make the oscar attack, knowing that I will poke the oscar with the tongs. But the oscar never does anything, and both will swim pretty much touching each other or with knife darting all around the oscar and no aggression. The knife will be eating off the bottom with its tail directly in oscars face even touching its eyes, and oscar wont react at all. At first after this treatment the oscar was scared of whenever i stuck tongs in and would go play dead in a corner, even if it wasnt to make him back off the ghost, but now it is not scared of them, and really just seems to know "dont fck with the ghost and there will be no problems." Oscars seem trainable.