“草泥马” is a Internet meme created by angry netizen, furious at current boring state of censored China Internet. The censored is aim at pornography. However, because of the ‘very intelligent’ filter, every thing that got flesh also kena blocked.
Hence the meme, Grass Mud Horse is Chinese vulgar equivalent to *ahem*, asking how’s your mother. Pardon me.
Here is the news(Link). NYT News here(Link). For whatever is worth, I hope there isn’t such horse.