Last week I gave you this unassuming cobble-like object to have a go at identifying:

What you can’t see is that this is actually a surprisingly lightweight object and it’s most definitely not made of stone – not even a stone as light as pumice.

It is in fact of zoological origin and it’s an example of an object I featured on the blog 13 years ago (almost to the day), when I worked at the Horniman Museum:

As Chris mentioned in the comments, and as Nigel Cook said on Twitter:

These are both trichobezoars – boluses formed from hair that form in the digestive track of an animal (usually an ungulate, although other animals, including humans can form them too). Bezoars are reputed to have magical properties and historically they were valuable high-status objects.

These two look quite different to each other and that is probably because one of them is fully mineralised (mystery object #442), while the other (mystery object #7) is barely mineralised and still has matted hair visible (and it still smelled pretty bad if I remember correctly).

I was going to add a little more information to my previous answer about these remarkable objects, but David Carter has an interesting article about them on the excellent Mindat website, so why reinvent the wheel? I recommend checking it out, as it’s well worth a read!