Of course, this simile is obvious when you see it, but have you ever seen it before?  Please try incorporating it into your simile-store.

‘Over fall he slid, smooth as oil.’

Source: Henry Williamson, Tarka the Otter: His joyful water-life and death in the two rivers, illus. C.F. Tunnicliffe (Harmondsworth: Puffin Books, 1976 (1927)), p. 89

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