Crossed threads

After recharging my battery and re-gapping my plugs I found that the rear-most plug wasn’t going in all the way when I attempted to hand tighten it. Are the threads crossed? I couldn’t tell. The plug hole is very close to the firewall making it hard to to see what’s going on in there. It’s possible to get a chasing tool that would straighten out the crossed threads, but I’ve been warned that using such a thing would run the risk of depositing metal shavings into the block which would be not good. I’m waiting to get my hands on an endoscope so that I can better see the situation before I do anything. I’m hoping the threads are just really dirty and this situation can be solved with a good brush cleaning.