When Yosemite Sam gets back to the door of his fort after taking the barrel of gun powder to Bugs' fort, the fuse is missing.
Sam burrows underground from his masonry fort to Bug's wooden stockade. When he emerges, it is in the powder magazine. He strikes a match and blows himself up. But just before it blows up, the view goes from inside the magazine to outside, and Bugs' fort is no longer a wooden stockade, but a masonry fort.
When Bugs tells Sam "Your brother blows bubblegum", his mouth is not actually moving, but instead just wide open.