From China Digital Space
Troublesome creature whose name echoes "harmony" (和谐 héxié); euphemism for censorship. Coined by netizens as a reference to the government's justification of censorship as an essential ingredient in constructing former president Hu Jintao's "harmonious society." In pre-Internet language, a crab is also a bully.
Both "harmony" and "river crab" can be used as verbs. Instead of saying something has been censored, you can say it has been "harmonized" (bèi héxié 被和谐) or "river-crabbed" (bèi héxiè 被河蟹了).