A line of metal

Original fiction extract.

The model bridge looked too heavy beside the little houses. I had built its supports from thick sticks because I was afraid they would break. The tutor showed me a slender metal rod lying beside the cutters. It was long but very thin across. We did not replace anything immediately; first we held it beside the model to compare the outlines. The river beneath the bridge became visible again. I took a photograph of both versions before deciding which materials to use in the final piece.

Use your own words to explain what the word “slender” means in this extract.