My Sun has started "knocking". He did it one night after I was done giving him scritches. He kept pushing his head up against my hand and when I wouldn't show him attention he started knocking on the computer desk. LOL He even bobs his head too. It's so silly. Right now he's in his cage and since I'm not paying attention to him he's making baby noises, bobbing his head and knocking on the cage. So cute!
Lately he has gotten REALLY jealous of my mouse and keyboard. Whenever I have my hand on the mouse he climbs on my hand and starts biting (gently). If I'm typing, he'll grab one of my fingers and try and pull my hand off the keyboard. ;p