"Holy Cow, man!"

I am not one of those folks who complains about every little typo in a book. And an author writing about an unfamiliar city might be forgiven for geography mistakes, I suppose.

But there are times when the author goes into an area in which I expect accuracy - and when I do not get it, it leaves me scratching my head in annoyance!

Case in point, the Enervate spell in HP that brings folks life instead of draining them.

I have been reading Joe Haldeman's Camouflage. One of our main characters is an alien being who has been on Earth for millions of years. He has recently come to shore.

*****
It was sundown, almost dark. The beach was deserted except for one man, who came running up to the changeling.
"Holy cow, man. Where'd you swim from?"
*****
(a little later in the chapter)
*****
Five teenagers came out of a burger joint with a bag of hamburgers.
*****
What is my objection?

This is taking place in San Guillermo, California in 1931!! Now, I suppose that there may have been a hamburger joint in California then, though I am skeptical. But not that likely... and "Holy cow, man" strikes me as very anachronistic! Even if the "Holy cow" part may date back to the 20's (though 1940's seem more likely), the addition of the 'man' at the end makes this not a 30's line, but a 60's or later expression.

Do I put too much into this? Well, sort of. I know that some of my readers would do the tracking of data if I did not!