What is the rule for using "mientras" or "mientras que"?
For example:
Escribo mientras que él come. Why can't I say: Escribo mientras él come.
Él habla mientras yo leo. Why can't I say: Él habla mientras que yo leo.
I cannot see any difference in syntax, usage or meaning between these two sentences, yet three native speakers have all told me they would only say the first, but could not tell me why or give me any grammatical rule. Please help... someone/anyone.