I read this a long time ago, and thought it was Larry Niven but maybe not.
A bunch of scientists build a gate to a parallel world and initially observe the inhabitants on the other side. They seem to be a typical Midwest rural family (I think that's the right description but I am a Brit ;-))
A couple of them step through and a little girl smiles at them, then her grin gets wider revealing sharp predator's teeth and she instantly attacks.
The family rips the travellers apart and throws their bones back through the gate.
The head of the household then retrieves a book and reads from it in the manner of a preacher, causing the gate to slam shut and thereby demonstrating both knowledge of gates and some form of magic.