Snake Expert Gives Horrifying Detail of Python Eating Woman

The shocking video aftermath of an Indonesian woman's death by python is creating more questions -- but a renowned snake expert knows what most likely happened, and it's the stuff of nightmares!

Here's the deal ... a massive 20-foot-long snake devoured a mother of 4 while she was walking through the forest to get to a market. As we reported, locals -- including the victim's husband -- later found the serpent, killed it and recovered her body.

Now, Mark O’Shea, host of the old Animal Planet series "O'Shea's Big Adventure," tells TMZ -- in disturbing, yet fascinating detail -- what most likely occurred when the reticulated python attacked.

Mark is confident the snake ambushed the victim near a game trail ... and immediately started coiling around her with its gigantic, powerful body.

He says she would've lost consciousness likely within seconds, certainly no longer than a minute ... which is a good thing, because as the python constricted, blood was pushed to the top and bottom of her body -- which resulted in a heart attack.

As with any meal, the snake started ingesting the woman by the head, so her limbs could go down smoothly.

While the death is a sad situation, Mark says fake social media clips of snakes eating people are far more common than real incidents. He says it's rare because snakes don't purposely hunt humans -- they just hunt when hungry -- so, it's a matter of being in the wrong place at a very wrong time.