This isn't a real danger, but if you don't like iguanas, be carefull where put your feet! In Tulum there are many iguanas. You can see them while they are basking in the sunshine. However they aren't dangerous. I like them very much.
Easy to get sidetracked in Playa del Carmen by timeshare sellers, who roam the main tourist areas offering free meals or cheap car rentals in exchange for attending a "brief" informational meeting. The meetings aren't brief, and the sales tactics once you get to their site are unscrupulous. DON"T GET TRAPPED!