As you've probably gathered, time travel is not as straightforward as it seems. When you attempt to alter the timestream, you risk unleashing unforeseen consequences.
Case 1: The Butterfly Effect of Bad Taste
John, a time traveler from the year 3050, visited ancient Egypt to sample some authentic 3000 BCE cuisine. He ended up with a severe case of Chrono-Gastritis.
Or, if you're feeling adventurous: