So Tony and Mario are working on a barn roof one day when the wind kicks up and knocks over their ladder. Being about 30 feet up they have no easy way to get down.
Tony peers over the edge, and sees a large pile of manure. So Tony says to Mario, "Hey, how about I jump first into the manure, and then I yell up to tell you how deep it is, to make sure it's safe."
Mario agrees, and Tony jumps. A few seconds later Mario hears, "OK, it's only knee deep, come on down!"
So Mario jumps, and the manure quickly engulfs him up to his neck.
Mario yells, "Tony, I thought you said the manure was only knee deep?!"
And Tony says, "Well I didn't know you were gonna jump feet first!"