The four sounds here are from "Casino Audio" (version 1.1) by Kenney Vleugels
(Kenney, https://kenney.nl/assets/casino-audio), released under Creative Commons
Zero (CC0 1.0, http://creativecommons.org/publicdomain/zero/1.0/): public domain,
free for any use. The licence is stated on the pack's page and in the pack's own
License.txt, which says "Credit (Kenney or www.kenney.nl) would be nice but is not
mandatory", and credit is given here.

They are the pack's files re-encoded as short mono 22.05 kHz WAV, trimmed and
levelled, so that every browser plays them:

  clack.wav   from chips-collide-1.ogg   a checker set down
  hit.wav     from chips-collide-3.ogg   a checker hit
  dice.wav    from dice-throw-1.ogg      the dice thrown
  cube.wav    from chip-lay-1.ogg        the doubling cube turned
