We used a Evenflo Chase Deluxe as a secondary seat in my mother's car. (Yes, I am aware that RF would be better, and he is RF in my car, but that's not the point here at all.) Today, ds leaned sideways while riding in the seat and his arm slid into the gap between the seat and the arm rest. It became entrapped and pulled him sideways enough that the harness caused an abrasion on his neck where it was pressed against it. By the time I noticed this- it had been a couple minutes, and he was having trouble remaining conscious and there was considerable jugular vein distension. He had been harnessed properly, and the chest clip was in the proper position.
I freed him from the harness and watched with great relief as he pinked back up with proper oxygen levels, however his arm remained trapped. After several minutes of manipulating his arm to try to free it, and liberal use of some vaseline to try to help slide it through it became clear that it simply wasn't coming out. Ultimately, we had to cut through the seat with a sawz-all and break it apart to get his arm loose.
It was a scary wake-up call that even the places we put our kids to protect them aren't always as safe as we like to think.