GUINEA PIGS CHATTER THEIR TEETH WHEN THEY ARE:
The answer is: angry. When guinea pigs get angry you will hear those teeth chattering. They also do this to show that they are the dominant pig in the herd.
FUN FACT: Guinea pigs also make "purring" and "rumbling" noises which sound similar to when they chatter their teeth but means different things. They purr when they are happy. Purring sounds like chattering their teeth, but you will notice squeaks and "wheeks" mixed in there. It almost sounds like they are muttering sometimes. Rumbling sounds almost exactly like teeth chattering but it is a lower, deeper sound. Only males make this noise, and only to attract female pigs attention.
A DEGU'S TEETH SHOULD ALWAYS BE:
The answer is: orange. Most of you got this one right. I may not have worded this question terribly well, because it really should be " an adult degus teeth should always be orange", because when they are babies their teeth are generally white, but should become orange once they reach adulthood. So an adult degu's teeth should always be orange. If an adult degu's teeth are ever white that indicates a problem and they should see a vet.
FUN FACT: Wondering why a degu's teeth are orange? When degus eat, a reaction occurs between the chlorophyll in the plants they eat and the saliva in their mouth. This reaction stains their teeth orange.
ANOTHER FACT: A degu eating a healthy diet should always have nice dark orange teeth. If their teeth are pale yellow, this could indicate that they are not getting enough hay and green vegetables in their diet.