"Harry, I ..." Severus sighed and closed his eyes. Taking his time, since he knew this man by now, the younger waited. "That year, I was ... angry, most of the time. I did more than adjust the potions. I wanted them to be stronger, better, but I did not have the knowledge I have now. A few became unstable. My adjustments made them dangerous. I mostly corrected these errors by the end of the year, but I don't know if everything in there is safe. Also ..."