The annual modulation signal observed by the DAMA-LIBRA Collaboration (D-L) may plausibly be explained as a consequence of energy deposited in the NaI(Tl) crystals by cosmic ray muons penetrating the detector. Delayed pulses in the approximate energy range of interest have been observed as a sequel to energy deposited by UV irradiation. The same behavior may be reasonably expected to occur for energy deposited by any source of ionization or excitation. D-L can test this hypothesis by searching for time correlations between muon events and pulses in modulation energy range in current data, and by renewed operation of the array at a sufficiently low temperature that would freeze out the phenomenon.