Cyanoacrylate is a moisture cure adhesive. You have lots of moisture in your skin which helps it cure.
Cyanoacrylate is used in medical glue because it bonds so well with skin.
Depending on the cut/injury, the medic may apply glue instead of stitches.
It’s doing its job. Don’t use acetone, it’s bad for you.
I scrape it off with a Stanley knife blade.
Not all cats have a problem with flaps.
I have two cats they have zero problems with the flaps. They sometimes use the flap as a short cut to sneak up on the other one when playing.
I have those electronic ones you register with their microchip so only they can use the flaps.
But, I still get gifts like mice, skinks, praying mantis, cicadas, leaves, etc. The flaps don’t stop gifts.