The Mishna on yesterday’s daf taught that if someone who was selling land stated at the time of the sale that he was selling an exact amount – according to strict measurements – then even a small amount would have to be returned or paid for. If, on the other hand, the seller said that he was selling “more or less” that amount, then even if there was an error of up to one-quarter of a se’a of planting (which is 1/24 of the beit kor field that was being sold), we accept that it is within acceptable error and it need not be returned. The Mishna continues that if the error was larger than that amount, the additional land would need to be returned, concluding ve-lo et ha-rovah bilvad hu maḥzir, ela et kol ha-motar – and he returns not only the quarter that was given in error, but the additional bit beyond the quarter, as well.
The Gemara reacts to this line in the Mishna by saying kelappei layya!? Shouldn’t it be the other way around!? The Gemara concludes that the Mishna should be worded otherwise – that not only is the small additional amount returned, but that the entire error must be given back, even the part that the purchaser could have kept had the error been smaller.
The term kelappei layya!? is usually interpreted to mean “where are you turning?” or, in this context “how can you think that, since it is the opposite of what appears to be logical.” There are Ge’onim who offer an alternative interpretation, explaining this expression as though it were kelappei alya – “towards its tail” – meaning that it appears that you are riding backwards, i.e. your statement is the opposite of what you should be saying.