NORTHAMPTON - All last week, students at Smith College were buzzing over a rumor that the school was going completely vegetarian and locavore. There were protests and counter-protests, with slogans chalked on walkways. There was a Twitter feed that caught the attention of VegNews, “America’s premier vegan lifestyle magazine.’’ At a student government meeting, the dining services manager came under attack: How did she expect students to pass their midterms without coffee?

But the Smith administration wasn’t really planning to ban meat, food from outside New England, or anything else.

The whole thing was a hoax - one in a decade of annual pranks perpetrated by professors Jay Garfield and Jim Henle as part of their introductory class in logic. The point is to teach rhetoric and argument, albeit in an unorthodox way. Logic classes get dry. Typically, students spend a lot of time working through inscrutable proofs on the chalkboard.

So Garfield and Henle try to liven things up by inventing a rumor just this side of believable, then assigning their 100 students to convince the campus that it’s real by whatever means the students think will be most effective - fliers, Facebook campaigns, word-of-mouth.

“It wasn’t even drug-assisted,’’ Garfield saidof the day the two hit on the idea. “We’re just brilliant and slightly weird.’’

The administration may agree with the slightly weird part. When people believe Garfield and Henle’s hoaxes - and some always do - trouble can ensue.

There was the time the professors planted the rumor that Smith, a women’s college, was planning to fire all of its male faculty members, including themselves. The president was deluged with angry letters.

There was the year of the alleged merger with nearby Mount Holyoke College, a proposal lots of students at Mount Holyoke took seriously, even as Smith’s scoffed.

And then there was the year of the supposed grass-roots attempt to start an ROTC program. Most of the campus didn’t fall for that one, but the president, Carol Christ, did.

“It was my first year, and I was just about to meet with the board of trustees,’’ she said. “I was like, ‘Oh, no, how am I supposed to handle this?’ ’’

As for the vegetarian/locavore imbroglio, about a third of Garfield and Henle’s students said they thought they had fooled the campus. After all, the college already makes a point of buying local veggies when possible, and the trustees had met the previous weekend - so in theory they could have OK’d the plan in secret.