Size-Changing Shoes

My sister had recently told me about a case of buying two pairs of shoes which she had to return because they were too large. It was a bit mysterious because she had been using this same label and size for years. Couple of days later I went to my yoga class. After the class I put on my shoes, hopped on my bicycle and headed for home. The shoes felt a bit weird. I glanced my feet and saw shoes which looked totally familiar. Then I absent-mindedly remembered my sister’s stories and though that shoes maybe change size sometimes. When I got home I inspected the shoes more carefully and noticed that their size is 42 when my size is 38. I had put on somebody else’s shoes!