Metaphor/Simile
In the lines provided, we see that Helena says to Demetrius that she is his spaniel. This does not mean that she is actually a canine, what is happening here, however, is that Helena is making a comparison between herself and how she is treated by Demetrius to that of a spaniel. In literature, when comparisons are made between two things that not alike in order to paint a better mental picture for readers, this is known as a metaphor or simile