Any ideas on possible cause of death?

My daughter's rat just died suddenly in a bizarre fashion, and I am wondering if anyone can help me figure out what happened.

She had 2 large males, littermates about a year old. The cage is a double-decker Critter Nation with fleece lining, lots of chew toys and tubes and tunnels, Mazuri block and fresh water. They have always been sleek and healthy. My daughter checked on them around 6:30 this evening and all seemed fine. At 9, she checked in on them again, and one of the boys was dead in the bottom of the cage.

There was no blood on the fleece, but his body was in a position like he just collapsed suddenly, legs in all directions. His head was at an odd angle and part of his spine was visible when my husband picked him up. Has anyone ever seen anything like this?

That is very strange... Could he have fallen?
I'm so sorry for your loss.

I don’t think he fell based on his position. The vet says she has seen rats at a year old dying suddenly of respiratory issues, so that was her guess. She said it’s not uncommon for other rats to chew on a body. We weren’t willing to do tests to find out more.

My daughter’s surviving rat has had playtime with my son’s rats and everyone seems to get along well, so we are hoping they can all 4 live together with the right introduction.

Yes, sadly, respiratory disease is very serious in rats and they can die fast. It wouldn't be a bad idea to bring in the rest of your rats to make sure their lungs are clear.