Parseltongue – the "gift" inadvertently passed on to Harry Potter by Lord Voldemort during his attack on him as a baby.
The hissing language is usually described as the ability to speak to snakes but could it also apply to other creatures of a reptilian nature? And if so, could that throw new light on a passage from The Goblet of Fire?
The particular scene in question takes place during the first task in the Triwizard tournament when Harry is on his broomstick facing down the Hungarian Horntail dragon – and Redditor Darkcollector has a rather intriguing theory about it.
Darkcollector's suggestion is that when Harry "hisses" at the dragon to come to him, and it immediately does so, it is obeying a command in Parseltongue.
We know Harry has instinctively spoken Parseltongue in the past without realising he was doing it – as a young child on a trip to the zoo with the Dursleys and against Draco Malfoy in the Duelling Club – so this could simply be another instance of that. Alternatively, Harry knows exactly what he is doing but it's just not made explicit in the book.
Either way, if true, it's yet another occasion when the Dark Lord's unintended gift has been used to protect the very boy he was so intent on destroying...