Giant Bubbles are item weapons used by Norm in Crash Nitro Kart. During Norm's boss race, his basic form shoots square bubbles behind him to try and stop the player from passing him. His inner half shoots circular bubbles behind him which are also to try and stop the player from passing him.
Neither version of Norm can throw their bubbles infront of them, so if the player manages to keep infront of them both, it's just a matter of getting around the track. If the player runs into a bubble, the player will wear it around them like a force field, and they will be prompted to jump up and down to pop the bubble. While these bubbles cannot harm the player, they will make the player a lot slower.