The hardest mode: all 80 sounds together, with no clue which category the next one comes from. Recognising an animal among other animals is not enough here, because the right answer may sit next to a drum or a helicopter. This is the category to come back to once the others have been played.
Eighty sounds across seven themed categories. In "Mixed sounds" any of them can come up, and the game repeats none until all eighty have been heard.
Yes. Each game is ten rounds, and when it ends the "Keep playing" button starts another set without repeating the sounds already heard. With the two game modes that adds up to several different games before they run out.