Crows can remember a human face for 17 years, and pass this knowledge through their murder (group).

We know animals communicate with each other, and the trend is we generally discover more and have underestimated what many animal species practice and can do.

Everyone agrees that homo sapiens and homo neanderthalensis have talked together and lived (and bred) together; what makes inter-species communication (assuming a translator or device) impossible?

No, I don’t think “universal translators” are outside the domain of science fiction; but I think us building a device that enables two-way communication between one species and us, is probably more likely than not.

[1]: https://urban.uw.edu/news/crows-hold-grudges-against-individ...

Which ideas, specifically, are absurd by your reckoning?

Very confident statements when know practically nothing substantial in this topic