These are the unfortunately unloved white or red-backed mice found swimming around our coastlines. They have been sourced back to the sewerage system, where girls have taken the cruel action of flushing them down the toilet after attempting to suffocate/kill them using an ancient vaginal squeezing technique.
"Wow, look at that sea mouse - the poor thing is all swollen up."
"I was out swimming with the guys and nearly ended up eating a red backed sea mouse."
"Yeah, of course I'll come away camping. My lass is farming sea mice this weekend."