Other mistake: In the second scene in the Gorilla Building, Elizabeth says, "Thank you, Jeff" while talking to Charlie. Thirty seconds later she says, "Thank you, Charlie."
Other mistake: When Gracie gets a heart and she is about to go into surgery she begins to talk to her Grandpa Martie. Watch his lips, he is mouthing her lines.
Answer: Presumably it's a favorite mascot of the group. There's likely no backstory per se, it's just something the filmmakers did to add to sense that these people have been together for a very long time.