人の手を刺す stab someone in the hand.
人の手に短剣を刺す stab a dagger in someone's hand.
What's the direct object in the second sentence? Is it just 短剣 or 人の手に短剣? I ask because in the first sentence the hand is stabbed (手を刺す) and in the second sentence the hand is also stabbed but 短剣を刺す would make me think the dagger should be the one who's being stabbed(even though that would make no sense at all). So did I make a mistake thinking just 短剣 is the direct object in the second sentence or is there another explanation?