_American Sex Machines: The Hidden History of Sex at the U.S. Patent Office_ by Hoag Levins is a collection of patents issued since the 1800s for inventions related to sex. One of the most fascinating aspects of the collection is its reflection of the attitudes towards sex during the various periods of time represented. Some of the devices are downright scary, such as an erection preventer which consists of a cylinder lined with sharp teeth. Recommended for those with an interest in the off-beat.

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