Above but that ripe hard acorn must surely weigh a pound or two to have impaled itself
On returning ….the plug is made of dry mud.
I thought about that too ... but you don't see many squirrels in Blackthorn bushes - not the most hospitable tree for them to climb ! I think you might be right about there being an insect egg inside the acorn ...Perhaps a squirrel impaled it, gnawed the top of it, was disturbed and an insect laid eggs in it and sealed the end with mud?
I thought of nuthatch, jays and so on, but they wouldn’t be able to force an acorn onto the thorn. Perhaps a squirrel could?