What's so funny?

I was making dinner while Robby was watching a cartoon. He was sitting very quietly on the floor and all of a sudden he burst out in a deep laugh. I wanted to see what was so funny, so I rewound the video. He was watching the cartoon Little Bear which has lots of animals. The duck was performing a magic show and making his cracker disappear. With the ducks back turned to the audience he would eat the cracker and make a munching sound. For some reason that was the funniest thing to Robby. I kept playing it over and over and he kept on laughing and laughing!