Do you think you’re an extravert or an introvert? To answer, you might immediately ponder how much you like going to parties and talking to strangers, or perhaps you’ve already got an answer given to you by one of those online quizzes that prompt such self-reflection. The trouble with these approaches of course is that they rely on honest insight and a hefty dose of subjectivity. Maybe you quite like parties, for instance, but nowhere near as much your best friend – does that make you an extravert or not?

A completely different approach that gets round these problems involves using a lemon – more specifically, concentrated lemon juice. This is a test with a long history in personality psychology and it’s really easy to try out at home. You’ll need a cotton bud (or what’s called a cotton swab or Q-tip in the US) with a short piece of thread tied exactly in the middle of it. Now place one end of the cotton bud on your tongue for 20 seconds. Next, put five drops of concentrated lemon juice onto your tongue, swallow, and then put the other end of the cotton bud onto your tongue for 20 seconds. Finally, take the end of the cotton bud out of your mouth and hold the cotton bud dangling by the thread. The idea is to see whether it hangs horizontally, or whether the end that you used after the lemon juice hangs lower because it is heavier.

If your reaction to the lemon juice made one end heavier this suggests that the juice caused you to salivate more than normal, which is a sign that – at a physiological level – you are an introvert. If the cotton bud is horizontal, this suggests you didn’t react much to the lemon juice and that you are probably an extravert.