Strange cat paw

[Ems2111]

Hello,

On Sunday my cat was in our garden and since then we noticed he was licking his paw a lot!

I then suspected he had a splinter and took him to the vets who couldn’t find anything so they then prescribed anti inflammatory medicine.

Tonight we inspected his paw and found strange black crust and what looks like a sore.

I just wondered if anyone had any ideas what this might be? I have attached photos. Would really appreciate any help at all.

Thank you in advance!

If you rub a damp/wet cotton pad on the dark crust does it stain red?
Just wondering if the constant licking has caused the sore and the dark could be dried blood?

Mine licked a hole on her own shoulder so they can definitely lick a hole through their skin.

Scab?