As a child growing up in our rather large turn-of-the-century family home I had a craving which horrified my family but apparently did no long term damage.
There used to be a product, the name escapes me, which was a greenish clay like substance used for cleaning wall paper. The stuff absorbed grease, smoke and common dirt when rolled over or rubbed on the wall paper and was reused until it lost its supple consistency.
When fresh out of the can, I found it to be a great little snack.
I have no idea what it was made of.
“but apparently did no long term damage.”
Uh...yeah.
*Obviously*

Once had a dachshund named Pica.
As a toddler I developed a taste for match-heads. I’d even struggle with my mom and cry to get to one that I spotted on the ground.
The doctor told my mother to force-feed me burned toast to ‘break’ me of the habit. I did stop - for awhile.
As a teenager, I’d buy books of matches and eat the burned heads in secret.
I stopped, but I still salivate when I see or smell a burned match.
Don’t know why.