On the Holyhead side just after the Britannia Bridge there is an expansion joint covering the full width of the road. It’s two strips of polished shiny steel located in a nice very fast bend. It is a 50 limit over the bridge so that is what you supposed to do, but it’s tempting to go a little bit quicker. In the wet it’s always a sphincter clincher but all that happens is the bike shimmies as you go over it as you lose and then regain grip in a fraction of a second. I have seen riders panic as they approach it but no need.