It is interesting how different nations have their dogs make different sounds.
An American dog goes Woof, a Czech dog goes Haf, a Dutch dog goes Blaf, and a Chinese dog goes Sizzle.
International Dog Sounds
Explanation
Explain Bear
Listen here, nimrod. The joke implies Chinese dogs end up as food, hence the sizzle sound. Because, you know, racist stereotypes. And you probably think Panda Express is real Chinese food, don't you?