(I assume you meant "acyclic graphs")

No, I meant acyclic paths - I am not at all sure that that is the correct term, but I meant something like "no branches" - there is only one possible path through the graph and it covers all the nodes.

And, well, point granted. Honestly I was expecting something like that, but I couldn't see where the problem was*, so I went ahead and asked the question.

... yeah, in retrospect this allows for silly things like "surely rocks must fall up somewhere in the universe."