The two seem to go together........blood and the cough. I'd guess it was from the first injection attempt. Sounds like you passed through a blood vessel and deposited a little tren from the needle on the way through.
Some say it's the benzl alcohol.......but most gear contains some b.a. and yet you only get taste/cough from fina. Personally I thinks it's the benzl benzoate used in most "magic solutions" to speed dissolving and as a preservative. Read up on this shit........"kills lice and scabies, not to be used on open sores".
Sounds like something that would make you cough when it hit the tiny blood vessels of the lungs, doesn't it?
Well, I still love tren, so I'll brave the occasional cough, even though it literally knocked me to the floor once.......failed to aspirate.....duh.