In the Doctor Who episode "Dark Water" (S8E11), hundreds of human skeletons are seen sitting in the eponymous "dark water", which Dr Chang describes as follows:
It's so cool. Look at this. We call it dark water. Only organic matter can be seen through it.
He demonstrates by putting his arm into a jar of the stuff; he's wearing a jacket and wristwatch, but through the water only his bare arm can be seen.
Given the way this stuff works, how is it possible to see the chairs that the skeletons are sitting on?
Obviously from the out-of-universe perspective, the reason is so that at first glance they seem like just normal skeletons and only later we realise there's something else around them. If they were apparently suspended in a sitting position mid-water, we'd realise much sooner that something was up. But what's the in-universe explanation, given the way this water works?