An Englishman, Scotsman and an Irishman are in France during World War II, they have been cut off from their unit and seek refuge in a barn. Later that night they hear a German patrol coming round, so they need to hide.
In the barn there are three large sacks, so they all agree to try hiding in them. No sooner are they all in their sacks when the Germans burst in the door, they see the three sacks and view them suspiciously.
They approach the sack with the Englishman inside and kick it, quick-witted the Englishman says “woof” in his best dog impression, and the Germans shrug and walk to the next one.
Reaching the sack with the Scotsman inside they kick that one, and following the Englishman’s example the Scotsman says “meow” in his best cat voice and the Germans leave it be.
Then they approach the sack with the Irishman inside, as with the others they kick it and the Irishman says “potatoes”.