A further variation from https://gist.github.com/jamesdabbs/a85fa5553df7dba0ba3dbb25f4cafe4b

💩 🚌👏 .rb

require 'thwait'

class Voice
  BASELINE = %w( there is no - poop ing - on - the  bus - )
  VOICES   = `say -v '?'`.lines.map { |line| line.split.first }

  attr_reader :voice_name, :rate

  def initialize(voice_name, rate)
    @i = 0
    @voice_name = voice_name
    @rate = rate
  end

  def perform
    mod = word == "there" ? "[[volm +0.2]] " : ""
    Thread.new do
      if word != "-"
        system "say -r #{rate} -v #{voice_name} \"#{mod}#{word}\""
      end
      advance
    end
  end

  def advance
    @i = (@i + 1) % BASELINE.length
  end

  def word
    BASELINE[@i]
  end
end

a1 = Voice.new('Kathy', 400)
a2 = Voice.new('Agnes', 400)

13.times do
  (Voice::BASELINE.length * 4).times do
    t1 = a1.perform
    t2 = a2.perform
    t3 = Thread.new do
      sleep 0.25
    end
    ThreadsWait.all_waits(t1, t2, t3)
  end
  a1.advance
end