This isn't really a joke but more of a guessing thing.
5 ants walking in a straight line...
1st says : Infront of me none, behind me 4
2nd says: Infront of me one, behind me 3
3rd says: Infront of me 2, behind me 2
4th says: Infront of me 3, behind me 1
5th says: Inront of me 4, behind me 1
How comes theres 1 ant behind the fifth ant?