"Medical Opinions" joke

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 like we learned in class."
Since they couldn't agree they decided to ask the old man. They approached the old man and one of the students said to him, "We're medical students and couldn't ignore 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'll tell me what you think?"
Then one of the students said, "I think it's Petry Syndrome."
And the old man said, "You thought, but you're wrong."
Then the other student said, "I think you have Zovitzki Syndrome."
And the old man said, "You thought, but you're wrong."
So they asked him, "So what do you have?"
And the old man said, "I thought I needed to fart. I thought, but I was wrong."