I love the way the French describe a perforation shift: un piquage à cheval. Sounds so very intriguing! I've always thought it was French for a knight's move in chess, but that, apparently, is "marche du cavalier". Piquage, I suppose, comes from the verb piquer, meaning things such as to prick, to stitch, so that would be the perforation bit. But what's the horsey doing there? And why would a piquer à cheval mean a saddle stitch? Hmm.
Oh, before I forget, this is what horsey did to my Arc de Triomphe stamp:
How could he!