Recently, Bowman et al. claimed to observe an absorption profile in the 21-cm signal at the high redshift, centered at z=17 (Bowman et al. Nature 2018). If confirmed by other experiments, this would be the first detection of the 21-cm signal from the cosmic dawn. But the observed signal implies a value of gas temperature even cooler than that allowed in the standard picture. In a companion paper, Barkana proposed a model to explain this, in which the interaction between baryons and dark matter particles further cools the gas. I will introduce these works in the informal talk.