Grudge expresses himself with grunts In the TV series, he has shown to care for Vendetta although she doesn't feel the same.
He has been shown to like pancakes in Smash. Sometimes when Grudge grunts, he expresses a sign of getting tired of doing what Vendetta tells him to do. Also in that same episode he attends the pancake festival without Vendetta knowing.
It is possible he is suffering from neglect, he even grunted when Charlotte said Buttons was "her favorite hamster in the whole world".
Grudge is a giant honey mustard colored hamster. His unibrow is considered to be more likely a miserable look.
Despite his name being Grudge on the show
and the Nickelodeon website the only one in the show who calls him Grudge is Charlotte. Vendetta only ever calls him Hamster. He is also similar to Buttons Charlotte's hamster.