yes, he has eaten some pieces of the pizza
Mr. Vu: I think it depends on the situation.
Generally speaking, yes, the simple past -- he ate some pieces of pizza -- would be preferred. But context could demand the present perfect -- he has eaten ... -- despite those pieces of pizza having been finished:Originally Posted by Mr.Vu
Yes, [Signor Cognoscente] has eaten some pieces of pizza [that most would hardly dare imagine] ... outrageous pizza
"He ate some slices of pizza earlier, so it won't matter if dinner is a little late."
"He has eaten some of the pizza! I can't serve a half-eaten pizza to dinner guests!"