Breakdown of Gähnend steht er im Flur.
er
he
stehen
to stand
im
in the (used with months) / in the (contraction of in + dem)
der Flur
the hallway
Questions & Answers about Gähnend steht er im Flur.
How is the word gähnend formed here?
It is the Present Participle (Partizip I) of the verb gähnen (to yawn). You form it simply by adding a -d to the infinitive. Here, it translates perfectly to the English '-ing' form: yawning.
Why doesn't gähnend have an adjective ending like -e or -er?
Because it is being used as an adverb of manner. It describes how he stands, rather than describing a noun directly. When a participle (or any adjective) is used as an adverb in German, it never takes any grammatical endings.
Why is the verb steht before the subject er?
German strictly follows the 'verb second' rule in main clauses. Because the participle gähnend takes up the first position in the sentence, the conjugated verb steht must take the second position. This pushes the subject er to the third position right after the verb.
Why is it im Flur instead of in den Flur?
The hallway (der Flur) is a fixed location where the action is happening (he is just standing there), not a new destination he is moving into. Because there is no change of location, the two-way preposition in takes the dative case. In plus dem contracts to im.