What couldā€™ve caused this? šŸ¤”

Black light makes pee (urine) glow yellow - but this mark does not rub off & is dated & might not smell enough for human nose. Cat pee (urine) is extremely corrosive & sticky (ugly stuff!!) and might still glow yellow upon black light. Might also be the mark of some human pervert on bedroom door. Might be some chemical used to clean deck surface.
 
I had a small dog (20 pounds), when we let her out she would do her thing, then come back and wait for us to open the door. If we didn't get it open fast enough,she would scratch at about that location. When she passed away (12 years old) I painted that door. Steel door,and it was in better shape than that door.
 
Any ideas as to what could've made this "mark" on the bottom of this door & frame? NOā€¦.it was not a dog. I'm open to ANY and ALL suggestions because I don't have the first dang clue. Yes, it's part of a case I'm workingā€¦.
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Almost looks like something poured isopropyl alcohol on the door and lit it up
 
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