Alright, My tank is right next to my desk, so when I am not focused on my computer, I like to watch my Oscars. And I have noticed that the bigger of the two every so often does this thing with it's tail, where it vibrates (lacking a better word) very quickly like a rattle snake tale. And this is always when it is close to the bottom, and nearly touching the other one....My first thought that this was like some mating thing or something, but then I remmebered they are still to young. But then I got to thinking that maybe it was a habit that a female (or male) does.

But I was curious if anyone knew what this little act was, or if it means anything.

Likely a rehearsal for mating or dominance behaviour.

I have observed a similar "rattling dance" in juvenile male Kenyi at middle tank level, male Oscar (I had no idea then of its sex) at substrate level, unsexed Severum (The Gold one) middle level, both sexs Convicts at substrate level, and in both sexs of my Rainbowfish (Red-Salmon, Lake Kutubu, Boesemani) also at substrate level.

Pepe
Santo Domingo

chirping or strut is common behavior of my oscar.
lip-locking too and i love watching them doing
their wares. i enjoyed most when they circling
around as if they were dancing on top of their
slate.

I personally think it can mean a few different things, and will depend on how,where and what the fish is facing. I know other fish do the same or some similar thing,for instance a great white shark (some but not all) will back down to a human that displays a ridged body and shakes like a Oscar. I didn't believe this until i watched it and I myself have made very large fish move away by doing sharp vibrating movements with my hand. i think it could be a threat, a mating display and many other things but we cant work out what. maybe I am wrong but on watching fish and my Oscars they do a shaking before fighting, and when attempting to mate. a new fish will do the same when put in a new tank and approached by another fish. a dog barks, to me it sounds the same but by the dogs eyes,body, we have a better chance to work it out. I think that simple shake can mean a lot to fish. Or am I mad.??)))

i think you may be right marcus.
i noticed when i put my 2 parrots into the tank with my 2 oscars, the parrots swam over to 1 of my oscars and the oscar just wagged his tail really fast, but i noticed the parrot swam off after this.
maybe its some kind of 'im the boss' type of thing