my green terror cichlid nips my tiger oscar on his head/side...but not

[stallionrose31187]

aggressively...why does he do this? I'm pretty sure my GT is a male, because when I first introduced him to my oscar, he was doing these shaking movements like he was having a seizure....he stopped, but now they follow eachother everywhere in the tank and the GT gives the oscar little nips on his body/head.....ideas?... preferably from a professional or someone with alottt of experience with cichlids.

 

[Phishy MAN]

the oscar is just in his territory and his just warning him to go away.