What constitutes an implied waiver of the Miranda rights?

"[A] suspect who desires to waive his Miranda rights and submit to interrogation by law enforcement authorities need not do so with any particular words or phrases. A valid waiver need not be of predetermined form, but instead must reflect that the suspect in fact knowingly and voluntarily waived the rights delineated in the Miranda decision. [Citation.] We have recognized that a valid waiver of Miranda rights may be express or implied. [Citations.] A suspect's expressed willingness to answer questions after acknowledging an understanding of his or her Miranda rights has itself been held sufficient to constitute an implied waiver of such rights. [Citations.] In contrast, an unambiguous request for counsel or a refusal to talk bars further questioning. [Citation.]" (People v. Cruz (2008) 44 Cal.4th 636, 667-668 (Cruz).)