How can I enforce aliasing with Audacity?
Here's a Python script that does what Matt L said:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""Enforce aliasing by reducing an audio-file to every n'th frame."""

from scipy.io.wavfile import read, write


def main(inputFilename, outputFilename, n):
    rate, data = read(inputFilename)
    write(outputFilename, rate/n, data[::n])


if __name__ == "__main__":
    from argparse import ArgumentParser, ArgumentDefaultsHelpFormatter
    parser = ArgumentParser(description=__doc__,
                            formatter_class=ArgumentDefaultsHelpFormatter)
    parser.add_argument("-i", "--input", dest="inputfile",
                        help="input WAV file", metavar="FILE")
    parser.add_argument("-o", "--output", dest="outputfile",
                        help="output WAV file", metavar="FILE")
    parser.add_argument("-n",
                        dest="n", default=2, type=int,
                        help="every n'th frame gets played")
    args = parser.parse_args()
    main(args.inputfile, args.outputfile, args.n)


It might not be audible at factor = 2.  Try other powers of 2.