(CBS) — There is a potentially deadly danger for your dog in the supermarket snack aisle.

The danger is not what is in the bag – it IS the bag.

There are supposedly “funny” YouTube videos of dogs with their heads stuck in snack bags. But to veterinarian Larry Fox, it’s no joke.

“This is really frightening to see,” Fox said, watching a video of the dog panic and struggle for air.

“That dog would have died had the owner not been there,” he says.

Dr. Fox never heard of dogs suffocating from snack bags, until his patient, a healthy young pitbull named Axel, died.

Nat Porcelli, and his wife, Pat, didn’t know Axel had gotten into a potato chip bag that was left folded shut.

“Axel was just a sweetheart, loved everybody, everybody loved him,” Nat Porcelli says. “My wife and I were having a cup of coffee, and I heard a thud. Went up to the bedroom and there was our dog Axel, laying unconscious, with his head in the bag of potato chips.”

It’s not known how often this tragedy happens, but a “Prevent Pet Suffocation” Facebook page has seen regular postings by heartbroken pet owners.

Fox explained what happens to a dog that has a chip bag stuck on its head: “They work as a valve. They seal off the air, you can’t tear through them.”

The Porcellis said that dogs don’t realize what is happening to them.

“The animals get focused on what they’re eating and don’t realize they’re losing oxygen. The bag collapses on them and they pass out,” Pat Porcelli says.

The Porcellis now securely store chip bags and cut open bags they throw away, to protect any animal that might nose around in the trash.

Some dog owners who’ve suffered a tragic loss this way want warnings on packages.

The Snack Food Association had no comment on that, but did recommend bags be stored securely with a bag clip and be disposed of properly when they’re empty.

The organization’s president and CEO says in his 21 years in the industry he’s never heard of an incident where a snack bag caused a dog to suffocate.