McDonald's sells more than 75 hamburgers per second, according to the Fiscal Times. The fast-food chain feeds 68 billion people a day – that's about 1% of the world's population. Business Insider went out to meet McDonald's employees to investigate – among other things – the most widespread and long-standing rumours surrounding McDonald's menus and restaurants. Here are 6 rumours that employees are tired of hearing1. There are anti-emetics hidden inside their burger buns... "so customers can eat more without wanting to vomit," says an employee.2. Their kitchens are dirty. Again, this rumour dies hard: "I was pleasantly surprised by the hygiene measures. There is a lot of rules, you have to be really careful. I thought it would be less strict," explains an employee, adding: "We have alarms on our time clock so we all go to wash our hands. We get extensive hygiene and food safety training."3. The Filet-O-Fish is actually not fish, but meat... Customers are very suspicions of the breaded fish, too. In reality, it is, indeed, fish – all good!4. There are rats and cockroaches in their restaurants. Once again, a fast-food hygiene rumour that dies hard.5. They re-serve unfinished food. One employee says that several customers have returned their trays, saying: "Someone took a bite of it." Again, this is a rumour. For burgers, an employee explains: "We use metal tongs to handle burger patties, which can tear them apart."6. Large drinks are the same size as medium drinks. Many customers have called it a scam. However, “it's actually not possible. In order to fill the cups with a drink, the customer presses a button that dispenses it accordingly. There's a button for each cup size: small, medium or large.”For more information, check out the video above.