Video: This Film Sucks! – The Science of Leeches

Tim Cockerill returns to take a  look at some leeches in a short piece produced for YouTube’s Geek Week back in August. If you’re a bit squeamish this probably isn’t for you!

We couldn’t really make a video about leeches without showing off their impressive feeding apparatus, a Y-shaped jaw packing in roughly 300 teeth! This was a tricky shot to achieve, we had to persuade the leech to attach to a glass plate, holding it in position by hand, allowing us to shoot from below with a macro lens. It was a great sight to behold once we finally got it and it certainly helps bring something to the film that you hopefully wont have seen elsewhere.

We also had to get some footage of a leech feeding, so we set one loose on Tim’s arm, shooting a time-lapse to demonstrate how much they can expand during the feeding. Once it had attached to feed, we were very much at the mercy of the Leech’s hunger as we couldn’t shoot the final shots until it had detached. As Tim mentions in the film, it’s not a good idea to pull or burn leeches off as this may cause them to vomit their stomach contents back into the open wound – not a good idea if you don’t know what the leech as been feeding on previously. The best course of action to take is to let detach when it’s good and ready.

We also wanted to dispel a common myth about leeches using anaesthetics to dull the pain the sensation of pain whilst feeding – as Tim reports there’s little scientific evidence to support this and he certainly reports to feel a stinging sensation as the leech feeds on him.

After about 3 hours the leech was finally full and very happily detached from Tim’s arm – during ‘the feeding’ the leech utilises an anti-coagulant (called hirudin) and as you can see in the film this prevents the blood from clotting, causing the wound to bleed profusely four a couple of hours after it’s detached!

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Too Hot to Handle: The Science of Fire Breathing

Fire breathing is not a hobby I’ve ever attempted to take up and that’s probably for the best – both for my own wellbeing and for that of those around me. However, I did recently have the pleasure of meeting Tim Cockerill – someone who has taken this up as a hobby and luckily is rather good at it. Actually, he’s ‘Doctor’ Tim Cockerill, because he’s also an entomologist, that’s correct, a fire breathing entomologist!

Anyway, we decided to make a short and simple film exploring the science behind his act, also known as the ‘human volcano’ – essentially a film that would look at the process of combustion and how this relates to the methodology of fire breathing.

We also made good use of our GoPro and strapped it to his head to get some awesome point of view fire breathing shots – you can see these in full below:

There was a bit of a struggle in deciding how to explain burning, we wanted to avoid the use of the ‘fire triangle’ – (often taught at school) because we didn’t want to make something resembling a dry educational film, but at the same time we didn’t want to get too bogged down in the chemistry of oxygen and how this relates to its reactivity.

In the end we settled for explaining what ‘burning’ really means – I think the word often leads us away from understanding / remembering what it means to burn something. Essentially it’s just the name we give to the chemical reaction between oxygen and a fuel, a reaction occurs and new products are formed (and energy is given off in the form of light and heat). In this case the fuel Tim is using is a hydrocarbon which he reacts with the oxygen in the air to form carbon dioxide and water (and the fire ball!)

So yes, we haven’t gone into the chemistry of oxygen and why it’s so reactive – but I think our explanation is sufficient for the purpose of the film – we wanted to attract people with the thrills of fire breathing and use this as an in-route to explain some of the underlying chemical principles.

I think it’s really easy to forget simple things like this and we often assume we know what we mean when we use an everyday term like burning. It’s only when someone calls you out and asks you to explain what’s going on that we may stumble and realise we don’t actually know as much as we assumed we did. The YouTube Channel Veritasium does a great job at highlighting common shortcomings and misconceptions when it comes to explaining everyday phenomena (watch the video ‘Misconceptions About Temperature’).