"After the accident, his neck hurt."
Translation:Post la akcidento, la kolo doloris lin.
In this lesson there was the English sentence and then Esperanto words to move around to make the sentence. There was no tile that had "lin" on it so I had to construct "Post la akcidento, la kolo dororis" without the "lin" and it accepted the sentence as correct. I think this is an error because "doloris" is transitive but I don't see any way to report it.
This one is tricky. Does the neck hurt someone (transitive) or is it in a state of hurt (intransitive)?
Different languages have different answers to this question, and Esperanto tries to accommodate several of them. That's why the correct answers don't seem to be consistent with one other.
I figure you should just use "doloras" whether you use it with an object or not (as in "Mia dorso doloras" or "La dorso doloras min"), and you should be fine.
(The use of "doloras" is one statement where listeners should be flexible and you shouldn't have to be lectured about proper grammar.) :)
A quick addition:
I've verified that dolori is technically transitive in Esperanto. Thus, when something is hurting, it means that it is hurting something.
Whether a dog is hurting me, or my shoes are hurting me, or my arm is hurting me, each of the subjects are doing the hurting, and in all those examples I am the object that's being hurt.
However, that last example ("My arm is hurting me") can be shortened to "My arm is hurting" (and even "My arm hurts") in both English in Esperanto. In both languages (and I'm sure in many other languages), when a body part is hurting and no direct object is supplied, it is assumed that the body part's owner is the object being hurt.
Therefore, "Mia brako doloras" ("My arm hurts" or "My arm is hurting") is likely short for "Mia brako doloras min" ("My arm is hurting me").
Normally we don't leave off direct objects with just any verb, but "dolori" used with body parts is different, as it's generally understood that the body part's owner is the direct object.
Post means after (as in time) sekve means following (as in cause and effect). There is a more clear line between them in esperanto than there is in English. In English you could say that there will be a lunch following class or there will be a lunch after class and mean the same thing. In Esperanto, the first sentence would assume that class caused lunch up happen. The sentence here is a little more muddy in the difference since the accident caused the pain but they were trying to convey time and not causation.
In the first clause the subject is him, but in the second the subject is his neck. The neck causes pain to him (lin), not to itself (sin). The use of reflexive pronouns isn't limited by number of people (or any nouns for that matter) but by whether the subject of a clause is the same as the object (and it's in the third person). If it is, then you use it.
I see you speak Italian and from some quick googling it looks like Italian has this feature as well. IT might be useful to compare those two.
Just in case the two comments get separated. The above content was intended to say kolo instead of lin.
The reason why is because kolo is the subject. It is the thing that is doing the action (hurting). The object (the thing being hurt) is him (lin).
The pattern of saying "the body part hurts me" is a common way to express that a body part hurts in several languages but it seems awkward to english speakers.