Learn Arabic (Modern Standard): حسبت الفخ تلميحا منطقيا.

This is because حسب (to assume/think) is one of the 'verbs of the heart' (mental actions) being taught in this lesson. These verbs take two direct objects instead of one. Here, الفخ (the trap) is the first object, and تلميحا (a clue) is the second object. Both must take the accusative case.

If I remove the verb حسبت from this sentence, what happens to the two objects?

If you remove the verb and its subject, the two objects revert to a standard nominal sentence (a sentence with a subject and a predicate). They would change back to the default nominative case: الفخ تلميح (The trap is a clue). Verbs like حسب essentially swallow a whole nominal sentence and turn its two parts into two direct objects!

Why does the adjective منطقيا take an accusative ending?

Adjectives in Arabic always copy the grammatical case of the noun they describe. Because the noun تلميحا is the second direct object of the verb, it is in the accusative case. Therefore, its adjective منطقيا (logical) must also take the accusative double fatha (-an) ending to match it perfectly.

Can the verb حسب mean something else besides assuming or thinking?

Yes! If it is used for a physical action rather than a mental one, it means to calculate, compute, or count (like counting money). When used to mean calculating, it acts as an ordinary verb that only takes one direct object, not two.