My parents live in a very old brick home in a warm climate.
They have owned their home for over 30 years and have no intentions of moving.
They had a brand new HVAC unit installed when they moved in, and have not had it replaced since then. One winter, my dad noticed a family of racoons living under the porch. They were harmless and not bothering anyone, so he decided to let them stay. They would come out at night crawl around on the porch. One night, we noticed that there were 2 babies missing from the family. We were sad but understood that they might just be staying under the porch. Well, we were wrong. The babies had climbed into the A/C unit and could not get out. We did not realize this until several days had passed. We started to smell a foul smell each time the HVAC system turned on. It got worse and worse as time went on. We did not make the connection that the smell was coming from the dead raccoon in the air vents! It was really an awful smell. We were so sad when we found out that the babies got stuck in the vents and could not get out. A few months later, another family of racoons showed up under the porch. My dad called the wildlife hotline in the town and had them come pick the family up so we would not have to deal with another situation like before.