a sockpuppet is someone who namechanges on their own thread.. so for instance:
Someone posts a thread saying "I gave birth to a baby last night and it had two heads and weighed 22 lb and I was up climbing a mountain this morning," and the rest of mumsnet all respond in a
manner, until another poster (the op under a namechange) comes on and says "How dare you question the validity of my friend's post, I am her rl friend and I guarantee she is genuine and you are all bitches and you all deserve to burn in hell..." 