In the following sentence, what is the phrase with the single participle: "Then, for no apparent reason, he let out a terrible cry, a rattle such as I have never heard before, and, his mouth open, thrust his head toward the steaming liquid."

A participle is a verb behaving as an adjective. Look at all the nouns in the paragraph. Then look at their adjectives; which is the only one that has a verb modifying it?