Whether it's the bottle of water that you hastily grab at the train station, or your favourite guilty-pleasure fizzy pop, you may have noticed something different about your drinks lately - or at least their containers. Since July 2024, it's been EU law that bottle caps are attached, or 'tethered', on all single-use plastic bottles. But what exactly is the reason for this change? Will it really help to save the planet, or is it just there to annoy us? We chat to Dr Diogo Veríssimo about "nudge", "sludge", and changing human behaviour for a better world.