A coworker got a deer during deer season in his shitty Nissan Altima. He put a tarp down and threw it in the trunk. Around early spring when the weather started warming up, he noticed a gross smell every time he opened the trunk. So he pulled the trunk liner and hosed it off; tons of red blood was washing out.

“Good,” thinking he had gotten it all.

By mid summer, no one would even park near the car the smell had gotten so bad. Riding in it meant you needed to have your head fully out the window to get any relief and usually required a change of clothes afterwards. This is when he really digs into it.

Removing the spare tire revealed 2" of congealed blood; looking a bit like a reverse Jello ring mold.

Yup, that was it. Smell took a couple of months to dissipated after the full cleaning, and he reportedly threw up only once. I was more amazed he managed to last ~7 months before he really started looking for the horrid smell.