of the resulting acid cloud was achieved by dripping water on a pilot light and melting ice over a hot pan. The whistling of the Seraphites was a long-discussed element of the game; production began in early 2018 in preparation for an upcoming demonstration. The team originally referenced whistled languages such as Sfryria and Silbo Gomero but found that they were more sophisticated than necessary. They also worked with a professional whistler but found the result too "birdlike". Dialogue supervisor Maged Khalil and UI artist Maria Capel recorded around an hour of sample whistles, which dialogue coordinator Grayson Stone organized into 14 groups dependent on duration, trill, intensity, and tone. After some iteration, the team decided on 26 categories, each representing lines the Seraphites use to communicate. Actors Stevie Mack and Lisa Marie provided the final whistles in three styles, each in a different level of quality. The team wanted the subtitles to represent the nuance of the whistles without giving away their exact meaning, and consulted accessibility specialist Morgan Baker to create them. The team discussed adding additional communication methods, such as knocking on trees or rattling, but it would have required additional animation, art, and sound design work. Release The Last of Us Part II was announced at the PlayStation Experience event on December 3, 2016. At E3 2018, Druckmann said that Naughty Dog was refusing to announce a release date until the game was "very close to release", to avoid disappointing fans. During Sony's State of Play presentation on September 24, 2019, Naughty Dog revealed that the game would be released on February 21, 2020. A month later, on October 25, Druckmann announced that the game was delayed to May 29, 2020, to "bring the entire game up to a level of polish we would call Naughty Dog quality". On April 2, 2020, Sony announced that the game was almost complete but had been indefinitely delayed to due to logistical problems caused by the COVID-19 pandemic. The team used the additional time for further polishing. In late April, several videos leaked online, showing cutscenes, gameplay, and significant plot details. Druckmann tweeted that he was "heartbroken" for fans and for the team, who had devoted years to development. A few days later, Sony stated that it had identified the leakers and that they were not affiliated with Sony or Naughty Dog. According to Schreier, hackers had used a