Here is the passage again:
While cleaning under his bed, Glen heard the vacuum cleaner suck up something
hard and metallic. Glen wanted to know what the object was.
But had no intention of digging through a bag of
dust, dead bugs, cat litter, and bathroom hair to find out.
The third part is a lonely verb fragment. This part has a verb, had, but no subject to keep it company. Every sentence must have a main clause which includes both a subject and a verb.