Certainly not a secret for an experienced cook. This technique is also known as butterflying.

It is occasionally used in restaurants when someone orders a well-done steak. You laterally cut the steak most of the way through, then flatten the whole thing.

For poultry, the French guys call this "en crapaudine" which is usually translated as "in the manner of a frog" (that's a misnomer since a crapaud is actually a toad). If you've had enough to drink, yeah, it sorta does look like a frog.

Good times, good times.