This might be persnickety, but "between" implies that there are two things that surround something.
In "A sheep sleeps between this" the word "this" stands for some unspecified object, animal, person, event, time, etc.
Think about this sentence: "The sheep sleeps between this child."
It doesn't make sense. It leaves you wondering: between "this child" and what else?
But these sentences do make sense:
"The sheep sleeps between these children."
"The sheep sleeps between this child and the fireplace."
In the same way, I don't think "A sheep sleeps between this" makes sense, but "A sheep sleeps between these" does.
Hay is an interesting example because hay, in English, is an uncountable noun. There is no plural of hay, there is just more hay.
English "in" can be within a single thing, but "between" or "among" require a plural.
"A sheep sleeps between this," as suggested in the first comment, is not correct English, because English and Dutch handle the plural rules differently.
Greetings, Gement & Jcbos.
When saying "this", my impression is somebody pointing at something near. Then what about, say, Brandenburg Gate, if I am pointing at it and I want to express someone is sleeping between pillars, can I say "Hij slaapt hiertussen de Brandenburg Tor" or "Hij slaapt hiertussen"?
I think that it might be to do with emphasis. I would guess that in "hiertussen slaapt een schaap", the emphasis is on the location that the sheep is sleeping inbetween, whereas in "een schaap slaapt hiertussen", the emphasis would be that it is specifically a sheep (and not, say, een schildpad!) that is sleeping between them?