You'll need to find matching pairs, where half of the matching pair appears to be missing.

Each of the words that Mr. Hincks yells has a letter that could be doubled to make a different word.

For example, you can double the "s" in "desert" to get the word "dessert."

Once you've found the missing letters, put them together in order to get the answer.

By adding the missing letter to each word, you get

"DESERT" => "DESSERT"
"NAN" => "NAAN"
"DINER" => "DINNER"
"HIS" => "HISS"

And the missing letters spell "SANS."