thumb|right|300px|Jump to about 0:58 to hear degus chittering (better video coming soon!)Chittering is a sound made by a degu when they are playing with their companions, it is made to let everyone else know that they are enjoying what they are doing and not to worry about them. If both degus are chittering, leave them be, they're playing together. If only one is chittering, and the other one is silent, they haven't decided if they wants to play or not. If they make any other noise it is usually directed at the chitterer and tells them how their actions are coming across. If you have many degus, you will probably find that there'll be times when one wants to play (and will chitter at all the others to see if they want to play too) and others react negatively with all sorts of sounds, this is normal too and you should only step in if the chitterer continues bugging the same degu despite negative responses.
If you have to step in, just go over to the cage and say "Noooo?" (not a definitive NO! but one that inflects up at the end) to the chitterer, if they ignore you say it a little bit louder and make the "oooo" last a little longer. If you are saying it loud enough and long enough that OTHER degus are coming to investigate but the chitterer isn't listening, then you have to step in directly and let them know who you're talking to...put your hand in the cage and go over to them to let them know...if they're friendly enough with you, play with them instead and try to get them to leave the other degu alone.
Chittering is one of the nicest sounds you will ever hear once you have had your degus for a while, it's a sign of contentment and comfort that only comes from a happy degu who is relaxed in their environment. Hearing all your degus making that noise is...well...you'll find out for yourself if you haven't already, and you'll never grow tired of it.