The figurative language used in this expression is referred to as an idiom. An idiom simply refers to the words or the phrases whose meaning can't be easily known based on the way the words are written. They're words that aren't taken literally.
They're just meant to create an image or have an effect on the reader. For example, saying someone has a cold feet simply means that the person is anxious or nervous and not that the feet of the person is cold.
Here, the dog eating an homework simply means that Daniel didn't do the homework and he's looking for excuses.
