How so? [If there were] fifty black figs and fifty white[ones], [and] a black [fig] fell [in], the black ones are forbidden and the white ones are per-mitted; [if] a white [fig] fell [in], the white ones are forbidden and the black ones are permitted. When it is not known what fell, they raise up one another. In this [case], R' Eliezer is stringent, while R' Yehoshua is lenient.