What does this joke mean?

This question is worth pondering. It should be like this. Rabbits also have many shapes. The front ones and the back ones all look good, but the ones in the middle are ugly all the time. After Li Si saw it, he couldn't say that sentence, and then it was like he didn't finish it. task (that is, he did not cooperate to the end), and then he could only say sorry to Zhang San. . . . so. . . That's it. Hope you are satisfied