UGC3995 is an interacting and occulting galaxy pair. UGC3995B is a foreground face-on spiral and UGC 3995A a bright background spiral with an AGN. We present analysis of the dust in the disc of UGC 3995B based on archival Hubble Space Telescope (HST) WFPC2 and PPAK IFU data from the CALIFA survey's first data release. From the HST F606W image, we construct an extinction map by modeling the isophotes of the background galaxy UGC 3995A and the resulting transmission through UGC 3995B. The inferred extinction slopes (RV ) maps do not display any structure and a range of values partly due to the sampling effects of the disc by fibers, sometimes due to bad fits, and possibly partly due to some reprocessing of dust grains in the interacting disc. To illustrate the difficulty of imposing a RV = 3:1 law over a section of a spiral disc, we average all spectra and show how a fully gray extinction curve is recovered.