Why is the manchineel tree dangerous?

The manchineel tree is dangerous because its sap and fruit contain poison. Its other name is Hippomane, which comes from the Greek and means 'causing horses to run mad'. The tree is a member of the Euphorbiaceae family and grows in tropical America, producing a crop of acrid, bitter apple-like fruits which drop spontaneously and carpet the ground beneath it. The sap is white and highly caustic, so that a drop on the skin produces a burning sensation and raises a blister. It used to be believed by many that to sleep beneath the tree meant certain death.