In the living room place some of your child’s soft toys in front of him. Blindfold and spin him around. Now re arrange his soft toys and remove one. Cover him with a large blanket. Tell him he must pass out a certain soft toy before he is allowed out. When he passes out the wrong one ask him to try again. See how long it takes him figure out that you took away the one he has to find.
You could try this with him crawling over not under a blanket.