Atlas can run.

That is what makes the doorway so difficult to understand.

The six-year-old Belgian Malinois mix moves normally around his shelter kennel. In the exercise yard, he can trot across open ground, turn sharply, accelerate after an interesting scent, and move from one side of the space to the other without obvious hesitation.

His legs work.

His balance appears steady.

His confidence can seem completely intact.

Then Atlas reaches a doorway.

One front paw crosses the threshold.

Then the other.

And he stops.

His back feet remain on the side he came from.

His front feet are already in the next space.

Atlas stands divided between two rooms.

His ears flatten.

His mouth closes.

The muscles along his back tighten.

Then his legs begin to tremble.

Sometimes he remains like that for several seconds, seemingly unable to choose forward or backward.

And if something suddenly makes noise behind him, Atlas does something even stranger.

He does not finish crossing.

He launches backward.

Within seconds, he is standing exactly where he started.

There Is Nothing Obviously Wrong With Atlas Until He Reaches the Threshold

That contrast is what first gets everyone's attention.

A dog with severe mobility problems might hesitate everywhere.

Atlas does not.

He can cross the kennel.

He can move outside.

He can turn.

He can run.

He can step over small changes in the ground.

But a doorway produces an entirely different dog.

The hesitation is not subtle.

Atlas can go from fluid movement to complete immobility in a single step.

Two Front Paws Seem to Be the Point Where Everything Changes

He usually approaches normally.

That matters.

Atlas does not always stop several feet away and refuse to come closer.

His nose can pass through the doorway.

His head follows.

Then one front paw crosses.

Sometimes Atlas still appears willing to continue.

The second paw lands on the other side.

His body stiffens.

The movement stops.

His Hind Legs Stay Behind

For several seconds, Atlas is physically split by the threshold.

Front half forward.

Back half behind.

It would take only another step to complete the crossing.

But that step seems disproportionately difficult.

His weight shifts slightly forward.

Then backward.

His ears remain pinned.

A tremor begins in his legs.

The open space ahead may be only a few feet away.

Atlas cannot seem to enter it.

Staff Initially Check the Floor

A doorway can contain many things a dog might dislike.

A raised threshold.

A slippery surface.

A metal strip.

A sudden change from concrete to tile.