Optical illusions, 4/5
\documentclass[tikz,border=10pt]{standalone}\newcommand{\cafestrip}[1][]{%\foreach \a in {1,...,6}{\draw[gray,very thick,fill=black,#1] (2*\a-1,0) rectangle(2*\a,1) ;\draw[gray,very thick,fill=white,#1] (2*\a,0) rectangle(2*\a+1,1);}}\begin{document}\begin{tikzpicture}%% the horizontal lines appear to slope\foreach \b/\c in {1/0,2/3,3/0,4/-3,5/0,6/3}\cafestrip[xshift=\c mm,yshift=\b cm];\end{tikzpicture}\end{document}