Answer

This requires quite a long discussion. As a rule, in order to remove an ox from its presumption of being non-forewarned, clear evidence is required. A presumption based on three occurrences is a presumption that serves as evidence to remove it from the presumption of non-forewarned status (without getting into the later authorities’ discussion of whether this is evidence or a new status being created; see Kehillot Yaakov, Tohorot, siman 47). For the evidence to be unequivocal, it must not be possible to attribute it to any parameter whatsoever, however slight. Therefore, if it gores only gentiles, there is room to say that its forewarned status applies only with respect to gentiles. There is no proof that it gores Jews as well. True, logic suggests that one should not distinguish, but there is no clear proof here. Therefore, even a slight basis for deferral is enough to undermine the presumption established by three occurrences. You can see examples of this in Yevamot 64b, in the passage about “the spring is the cause”; look there carefully.

Beyond that, one must discuss what exactly the case is. Everything I said applies if on three days it saw gentiles and gored them. But what if in between it saw Jews and did not gore? For example, if on day one it saw a gentile and gored, on day two a Jew and did not gore, on day three a gentile and gored, on day four a Jew and did not gore, and on day five a gentile and gored—then clearly this is even stronger, although one could still attribute it to odd-numbered days. It is worth looking at Kehillot Yaakov, Bava Kamma, siman 29—“forewarned for its own kind.”