Misc: What was the instrument of execution during the 'Reign of Terror'?

Questions

There is just one known species of ---------- in the world - it is in the order of Struthioniformes.?

The ----------, often called "possum," dates back over 45 million years.?

The famous cow used as the corporate symbol on all Elmer's products is actually named ----------, and she is the spouse of Elmer, the steer who the company is named after.?

There is no mention of cats or rats in the ----------?

The optimum depth of water in a birdbath, says the Audubon Society of America, is two and a half inches. Less water makes it difficult for birds to take a bath; more makes them ----------?