Oak galls (or oak apples) are formed by the oak gall grub. The grub wraps itself in this protective layer while it transforms into a wasp. It then eats its way out leaving a little hole in the top. During Tudor times oak galls were collected and ground down into a powder to make ink. 

My favourite items were oak galls because you can make ink out of them! Fascinating!

The oak galls were my favourite because i did not know that you could use them mixed with wine or water to make ink.