Simon

en.wikipedia.org/wiki/Metallic_hydrogen could be a good candidate. See also en.wikipedia.org/wiki/Metallic_hydrogen#As_a_rocket_propella‌​nt.

Typo: "can very continuously" -> "can vary continuously". I cannot edit it in because it is less than 6 characters, so in case someone else is doing an edit, please correct.

I cannot answer since I do not have enough reputation: Yes, a computer can be fooled. There are practical attacks on machine learning algorithms commonly used in AI. See for example blog.openai.com/adversarial-example-research and the images included there (for example a panda that gets misidentified as a gibbon).