What is Xiao Haiyang's goat joke?

Xiao Haiyang: "Once upon a time, there were a pair of goats. One night, they ... when the ram suddenly found out ... he asked the ewe,' Why is it missing?' The ewe said,' The shepherd's ...' "

Li Shu's words: "What is the shepherd's?"

Xiao Haiyang: "The shepherd's is ... it doesn't matter. Then, the ram said angrily, "…" At this moment, the ewe said very grievance, "…" "

Then Xiao Haiyang himself smiled: "I blush every time I finish this joke." Then he laughed hysterically.