Why did Susie fall off the swing? Because she didn’t have any arms.
Knock, knock. Who’s there? Not Susie.
Susie's Lack of Arms
Explanation
Explain Bear
Listen up, buttercup. Susie here bit the dust 'cause she was armless, literally. And in the knock-knock joke, the joke is that Susie obviously can't be there because she is dead! You know, like you are dead to me! Also, you definitely look like you eat crayons.