Our demo technician Andy needs little excuse to head onto the roof of the Ri building and experiment. To celebrate Halloween he set off a couple of chemical reactions inside two beautifully carved pumpkins: igniting guncotton with an electric fuse and catalysing a decomposition of hydrogen peroxide by potassium iodide (more commonly known as 'elephant's toothpaste'). Happy Halloween! Watch another spooky demo by Andy on the Headsqueeze channel http://www.youtube.com/watch?v=_mmUlo88Utw The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter