What has a neck but no head?
Published , last checked . Re-solved cold against the published wording before it went live: how puzzles and answers are checked.
A clean one-liner riddle with a concrete answer. From the free puzzle set on Think Fanny. Next try Two coins add up to 30 cents.

Why a bottle counts
If the answer feels like a stretch, the dictionary is on its side: a neck is any narrow part below an opening, not only an anatomical one.
If one of these contradicts the answer above, we would rather hear it than not. See how puzzles and answers are checked.