Jul 17 - Subject and Verb Placement in Questions

Doing some Spanish lessons, I noticed the different word order in the following questions:

1. "¿El perro nada?" (translation: "Is the dog swimming?")
2. "¿Duerme ella?" (translation: "Is she sleeping?")

I was wondering why one question (¿El perro nada?) has the verb after the subject and the other question (¿Duerme ella?) has the verb before the subject? In other words, why not "¿Nada el perro?" and "¿Ella duerme?". Does the order matter? Is there a grammar lesson I can learn here?

P.S. The only differences I can come up with are that sentence 1 seems to be a transitive use of the verb and sentence 2 seems to be intransitive use; and, sentence 1 has a definite article preceding a noun and sentence 2 is just a lone pronoun. I don´t know if any of this is relevant, just trying to learn. Thank you.