As a pox virus fuses with a cell it has just infected, it discards the shroud-like covering it uses to “hide” as it spreads from cell to cell within the body (below, green). The complicated tracks of protein-crystals seen on a “naked” pox virus (right, without shroud) mix after fusion with the cell membrane, making the collection of “mulberries” (below, blue). The event is captured using “quick-freeze, deep-etch” electron microscopy, a process created by John E. Heuser, MD, professor of cell biology and physiology, which lets biologists take detailed pictures of fleeting events inside living cells.