Dave wants a job as a signalman on the railways. He is told to meet the inspector at the signal box for an interview.
The inspector asks "What would you do if you realised that two trains were heading for each other on the same track?"
Dave says "I would switch the points for one of the trains".
"What if the lever broke?" asked the inspector.
"Then I'd dash down out of the signal box" said Dave "and I'd use the manual lever over there".
"What if that had been struck by lightning?"
"Then" Dave continues "I'd run back into the signal box and phone the next signal box".
"What if the phone was engaged?"
"Well in that case" persevered Dave "I'd rush down out of the box and use the public emergency phone at the level crossing up there".
"What if that was vandalised?"
"Oh well then I'd run into the village and get Nev".
This puzzles the inspector, so he asks "Why would you do that?"
"Because he's always wanted to see a train crash".