Greasy Fork is available in English.
By Kaushik-Rajarathinam
// ==UserScript==
// @name Slither Boost Audio
// @namespace https://slither.io
// @version 3.1
// @description By Kaushik-Rajarathinam
// @author https://github.com/Kaushik-Rajarathinam
// @noframes
// @match http://slither.io/*
// @match https://slither.io/*
// @run-at document-body
// @grant none
// ==/UserScript==
(function() {
'use strict';
//uses an audio from andrew bramwells website.
var audio = new Audio('http://www.andrewbramwell.co.uk/SMB-SP.mp3');
window.addEventListener("mousedown", function () {
audio.play();
}, false);
window.addEventListener("mouseup", function () {
audio.pause();
audio.currentTime = 0;
}, false);
})();