I have seen birds, lizards, frogs, fish, etc in various places on their back dead. May be insecticides cause them to flip over but I do not believe every upside down creature died by poison as stated in this question's answer: Why do cockroaches flip over when they die? and the roach question only covers roaches and insecticides. My question covers all animals not affected by poison that are belly up.
Other than poisoning is there any other reasons like DNA programming on behavior or muscle spasms that cause this?