Here's why:
* Verb: "Burble" means to make a bubbling sound, often associated with water or speech.
* Past Tense: "Burbled" describes an action that happened in the past. For example, "The stream burbled merrily."
* Past Participle: "Burbled" can also be used as an adjective, describing something that has been made to bubble. For example, "The water in the pot burbled and bubbled."
Therefore, "burbled" can act as a verb in its past tense form.