Question: There was another sentence (I think in present verbs 2): "Jeg rører ved hatten." and in this instance the verb "røre" needed the preposition "ved" because it's an intransitive verb (according to comments on the exercise).
Is it any different in the past tense? Is this a case of bad grammar that we shouldn't learn/emmulate? Or is adding the "ved" sort of optional?
In both "han rørte skildpadden" and "jeg rører hatten" the "ved" is optional. Most danes, including myself, would add it but it is not mandatory, and if anyone tells you otherwise know that this person is the danish equivalent of an englishman telling you that you can't end a sentence with a preposition. The fact is, english speakers do end sentences with prepositions and danes mostly treat "ved" as an option.
Mostly, but not always. In "han stod ved en bil=he stood by a car" the "ved" is necessary because "han stod en bil=he stood a car" is nonsense.