Masechet Eduyot (Tractate Eduyot), perek zayin (chapter seven), Mishnah bet. In the times of the Mishnah, they would eat grasshoppers. Actually, even some people nowadays, including the Yemenite community and others, eat kosher grasshoppers as well. There are two different types of grasshoppers. Some of them would be kosher, and some of them would not be kosher. But these grasshoppers, in order to make them edible, would be pickled in salt for a while. That salt would draw out all of the liquid that was inside the grasshopper in order to preserve them. The question becomes: Is that fluid, that liquid that was drawn out of the non-kosher grasshopper, kosher to be eaten or not?
The Mishnah says, “He'id Rabbi Tzadok al tzir chagavim teme'im shehu tahor.” Rabbi Tzadok testified that the liquid of a non-kosher grasshopper is kosher. The grasshopper itself is non-kosher, but the liquid is kosher. It's permitted to drink or eat that liquid. It's not considered to be part of the grasshopper. It's a separate entity. It's not considered to be blood either. It's its own unique type of thing. Therefore, it is permitted and it is pure.
The whole idea of Rabbi Tzadok testifying was to undo an earlier teaching, an earlier version of the Mishnah, before Rebbe Yehuda HaNasi organized everything, Torahs. The earlier teaching was that if non-kosher grasshoppers were pickled together with kosher grasshoppers, then the fluid, the liquid of that non-kosher grasshopper, would not make the kosher grasshopper forbidden. The mixture of both of them is permitted for consumption. But we see from here, we infer that only the mixture of the fluids is kosher, while the non-kosher grasshopper liquid on its own would be forbidden. Therefore, Rabbi Tzadok had to come and correct it and say that the fluid of the non-kosher grasshopper would be permitted even on its own. The earlier Mishnah told us that Hachamim (the sages) made a decree against the fluid of a non-kosher species, and they said that it's all forbidden. But they allowed the mixture because, at that point in time, it's a little bit far from the actual non-kosher grasshopper. Therefore, the mixture of them would be permitted. But again, Rabbi Tzadok came and undid that teaching.