What dish of fermented fish is traditionally consumed during Christmas in Sweden?

Surströmming

Which animation studio created "Wallace and Gromit"? Which fish is famously known for 'cleaning' algae off aquarium glass surfaces? What country celebrates Christmas by exchanging books and spending the night reading in a tradition called Jólabókaflóð? What was the U.S. foreign policy aim described as "containment" directed against? What did Jesus ride into Jerusalem just before crucifixion?