I was stitching on the red scarf at crochet class and I thought I noticed that it seemed to be getting narrower. I counted and recounted the stitches, but they were the same at the top, the bottom and even a few places in the middle I counted just for good measure.

I’m using the same hook. It is the same number of stitches. It is the same skein of yarn. I was not (as far as I can tell) any more tense while I was working on it. This one has me puzzled.