Answer we always started with the easy [words] i had already learned, and which i wrote down and read from the slate. the new ones i had to listen to first, putting them together as well as i could from the sounds. at the end of the lesson i had to listen to the formidable words that sounded more like trapezes in full swing. reread the simile. describe how it you see and understand what the author is experiencing

Formidable means frightening, so that suggests that the character has a negative mood toward learning the words, meaning that the character does not like learning them. And since she/he already sets a negative mood towards learning the words, we can say that she/he thinks of "trapezes in full swing" as terrifying or not entertaining. So when she/he says that the words sounded like trapezes in full swing, she/he might be suggesting that he sees the words as confusing or hard to learn.