이게 뭐야? (normal situation) What is this? 뭐야 이게?(abnormal situation) WHAT the hell is this? As you know, 이게 뭐야? is normal sentence. 뭐야 이게? is an inverted sentence. The inverted sentence is used for emphasizing the word 뭐.

the order of the words are not so important in Korean, especially when it comes to speaking. 이게 뭐야, 뭐야 이게 both are correct when speaking. but you have to write subject first when writing. 선생님, 안녕하세요. and 안녕하세요, 선생님. both are correct. 요즘 한국어 공부해요? 한국어 공부해요 요즘? 한국어 요즘 공부해요? all is correct...

same thing, but 뭐야 이게 is more used in a surprising situation. order in the sentence isnt that important in Korean as 다영 said, so 너네도 이거 하지? 너네도 하지 이거? 이거 너네도 하지? 이거 하지 너네도? 하지 너네도 이거? 하지 이거 너네도? all are correct, but the first part of the sentence is emphasized like Yesterday, Smith break the window. Smith break the window yesterday the window was broken yesterday

I guess they are just as "illogical" as the rest of us ;) ㅋㅋㅋㅋ