10 MORE Doctor Who Episodes You Didn't Know Were Connected
3. The Ark In Space & Kill The Moon
In one form or another, the yo-yo has been entertaining human beings since 500 BC. Its insane longevity might explain why so many different versions of the Doctor have carried one over the years.
The Fourth Doctor frequently used one to keep himself happy during his downtime. It wasn't all fun and games though, as this yo-yo had some practical applications that came in handy on certain adventures.
In the Season 12 story The Ark in Space, the Doctor uses a yo-yo to test the gravity immediately after landing on the titular space station. A good idea, seeing as gravity is kind of integral to the yo-yo's design!
This was such a clever move that the Twelfth Doctor repeated it nearly 40 years later. In Kill the Moon (the one we don't talk about), the Doctor uses a similar trick to study the odd gravitational changes of the Moon.
Sadly though, the yo-yo didn't tell him the Moon was an egg. Everyone had to find that out the hard way.