which medical condition?

[Sniper]

Two medical students were walking along the street when they saw an old man

walking with his legs spread apart. One of the students said to his friend:

"I'm sure he has Petry Syndrome. Those people walk just like that." The

other student says: "No, I don't think so.. The old man surely has Zovitzki

Syndrome. He walks just as we learned in class." Since they couldn't agree,

they decided to ask the old man. They approached him and one of the students

said to him: "We're medical students and couldn't help but notice the way

you walk, but we couldn't agree on the syndrome you might have. Could you

tell us what it is?" The old man said:"I'll tell you, but first you must

tell me what you think." One of the students said: "I think it's Petry

Syndrome."

The old man said:"You thought.......... but you are wrong."

Then the other student said: "I think you have Zovitzki Syndrome."

The old man said:"You thought.......... but you are wrong.

So they asked him:"Well, what do you have?"

The old man said:"I thought it was GAS........... but I was wrong!"