The scene is perfect to illustrate how the [u: ʊ] contrast can be challenging to speakers of languages that have only one high back vowel, such as Spanish (character Gloria's native language) and Portuguese (my native language). Therefore, no matter what Gloria is trying to say, "Luke" or "look", the boy (Luke) always understands "look".
I particularly like it when Gloria says, "I don't hear the difference", which shows that first foreign language learners need to be aware of the two sounds perceptually. EFL/ESL teachers need to help those learners create two phonetic categories, one for [u] and another for [ʊ], where there is only one in their native language.
I also like it when Luke explains the difference by saying that "one is my name". It shows that contrasting sounds of any language are so easy to be noticed by its native speakers that they simply focus on the meaning, and not on the articulatory action to produce those two sounds. It is like an English speaker with difficulty to make the [paw] [pãw] contrast in Portuguese, and a Brazilian saying that it is easy because one is something you eat.
Luke-look is actually one of the very few minimal pairs with [u: ʊ] (fool-full, pool-pull, cooed-could are a few others), and the spelling does not help a lot with the choice of the correct sound. There are many words spelled with "oo" that sound [u:] and other that sound [ʊ]. Take the simple phrase "good food", for instance. Both words end in "-ood", yet "good" is pronounced [ʊ] and "food" [u:]. Here is a small list of words spelled with "oo" and their appropriate vowel sound.
Stay tuned for more videos, and if you have a suggestion of a video clip I could use to illustrate a feature of English or Portuguese phonetics, please send it to me.