Well teaching your pet rat tricks is sure fun there is no pacific thing of saying just give them a little treat and not like they care just say "Yay" Or something but obviously they dont understand when you say something its a way of you happy f them like whem mine do tricks cause i am proud i come out and say something to them
I've heard of some people making an 'eep' noise if they have a nippy or slightly agressive rat that likes to taste them occasionally. It mimic's the sound that a rat makes when its not happy about something. Im not so sure about good sounds though. Maybe some of the pro's will know
Hugo bruxxes and stares at me when I babytalk to him XD I think they just learn to associate certain sounds with good things, and eeps or "tsst!" noises help in discouraging something, if only for a second heh