Why are gram and grim shouting while max was rapping the Christmas presents?

Gram and Grim are likely shouting in response to Max's rapping of the Christmas presents because they are excited or amused by his performance. Their reactions may reflect their enthusiasm for the holiday spirit, creating a lively and festive atmosphere. Alternatively, they might be playfully teasing him or getting caught up in the fun of the moment, contributing to the overall joy of the occasion.