A leg (still attached to a living body, of course).
Break each of the pills in half, as you do this pop one half in your mouth and lay the other half aside for tomorrow. When he's done this with all four pills he will have consumed one red pill and one blue pill. And have the same left over.
As there is no day when both of the beings would be lying, at least one of them must have spoken the truth. They both speak the truth only on Sunday. However, the Lion would then be lying in his statement, so it couldn't be said on Sunday. So exactly one of them lied. If the Unicorn was honest, then it would have to be Sunday - but previously we proved this wrong. Thus only the Lion spoke the truth when he met Alice on Thursday and spoke with the Unicorn about Wednesday.
Sword making a wound. The white rock is the bones. The red river is the blood.