What does a constant signal sound like? Say I was sampling a sound incorrectly and it produced a constant signal as below:

What would this signal sound like? In Matlab, it plays nothing. Is this correct?
 A: Matlab's silent output is correct. Physically, sound is a fluctuation of the molecules in some medium. If your waveform is perfectly constant, it corresponds to constant pressure: no fluctuations, meaning no sound. If it's very nearly constant, you will probably still be unable to hear the corresponding pressure wave without the aid of significant amplification.
Edit: In response to the quick comments above, an aliased signal is not generally silent, only in the extreme case when the wave is sampled at the same level each time. More typical undersampling will just result in a different sinusoid with possibly different amplitudes or frequencies than your original, thus the name "aliasing": the sampling process gave some new "name" to the original wave.
A: Admittedly this isn't really physics-related, but I found something amusing in Mathematica when trying this:
Play[Sin[8000 2 Pi t], {t, 0, 2}]


Mathematica by default samples Play at 8KHz, so it just gets floating-point aliasing noise when it's told to sample an 8KHz note (which it then gleefully amplifies to an audible level, resulting in something which is remarkably stupid-sounding).
A: This should sound like a sine wave. 
However if your cycle is too long, it is not audible to the human ear. To be audible, the cycle should be over 20Hz, or 20 times a second.
