The underwater scenes of Harry Potter and the Goblet of Fire (those, to be clear, related to the second round of the Triwizard Tournament) were anything but a walk for the protagonists, who found themselves acting immersed in a huge tank complete with blue screen for even rather long and demanding sessions.
To get an idea of what you think, for example, that the only Daniel Radcliffe remained immersed for 41 hours and 38 minutes (not in a row, mind you!) during the filming of the film, naturally assisted like all his colleagues by regulators that allowed them to breathe underwater without particular problems.
Despite this, nothing prevented the good Daniel from taking a shot at the rest of the crew present on the set: at a certain point, in fact, the actor inadvertently launched the emergency signal to the crew members waiting on the surface, who panicked and immediately brought him back to the surface believing he was drowning.
In short, a small mistake that certainly contributed to make you more adrenaline the day of the insiders! Speaking of Daniel Radcliffe: recently we proved how perfect he, Grint and Watson were for their roles in Harry Potter; Tom Felton, on the other hand, joked about the rivalry between Draco and Harry in a post on social media.