Oscars (most fish come to think of it) associate someone coming to the tank with food, so they get ready excited and dance about ready for it

However if you gonna do tank maintainence and put your hand in the tank they either recognise this as something bad is gonna happen (like being netted) or they see it as a possible predator that might try to get them, understandable really

My fish initially move away from the gravel cleaner when i put it in the tank to do a water change but once they realise what it is they swim around it like it isnt there. Its only when i move it that they move away from it

The yawning thing is normal, my oscars and some of my other fish do it occasionally