Hallucinations have been recorded for centuries both arising from illness and from consumption of certain substances, but what exactly are they? On the show this week we talk to Associate Professor Joel Pearson from UNSW about recent research that characterises hallucinations in a way that shows their origin, and a way to quantify them so they can be studied with greater accuracy. Here's a link to the video used in the study, WARNING: people who are at risk of seizures should not view this video. Claire talks about one of the suckiest invertebrates around, the haemophagic leeches.