ellipsis

Words can disappear

Not only do sounds disappear but often entire words are not said. 
In casual speech auxilary verbs in questions are often not enunciated. In casual speech the above might be spoken as:
This is called ellipsis and it's a common feature of casual speech. Perhaps if you were chatting with Queen Elizabeth you might not speak like this. However the average speaker certainly talks like this, especially if chatting with friends. 

"Have you got the time?" becomes "Got the time?"

"Did you see her last night?" becomes "You see 'er las' nigh'. "

You might think this is lazy English, or perhaps even bad English. But it's not. It's just plain old simple natural English. And our students need to know. Teach your students about ellipsis.