Should UK citizens vote to leave the European Union on Thursday, the market swings will last weeks, not months, according to one expert. 'I think [Brexit] will cause a short-term callous in the markets,' said Craig Erlam, a senior market analyst with Oanda, based in London. 'No one knows what the EU will look like without the UK and they don't know what the UK will look like when it's not in the EU.' He said there are also political implications of a Brexit, as anti-EU parties may gain steam throughout Europe. TheStreet's Scott Gamm reports from Wall Street.