Models of light pseudoscalar fields coupled to electromagnetism are quite common in theoretical physics. They predict "optical-activity-type" phenomena, if polarized SM particles propagate over region with non-vanishing gradients of such fields. Recent observation of the curl-type patterns in the CMB polarization require a second look at these models, as possible alternatives to the tensor mode origin of B-modes. I will show how massless pseudoscalar field fluctuations generated by inflation lead to a very specific pattern of the BB correlation, which can be compared with recent observations. I will also argue that massive pseudoscalar fields can also lead to a similar mechanism, if there exist stable remnants in the form of the domain walls of axion-like fields. Recent experimental activity to initiate the search for such domain walls will be described.