CDCl3 is a common solvent used for NMR analysis. It is used because most compounds will dissolve in it, it is volatile and therefore easy to get rid of, and it is non-reactive and will not exchange its deuterium with protons in the molecule being studied. It is also "silent" in the NMR and will not show peaks to interfere with the analysis of the compound of interest. However, whenever CDCl3 is used as an NMR solvent, a small singlet is always observed at 7.26 delta. What is this peak due to and why the heck is it there?