Interlocked Snake Knot

I call this knot interlocked because each half turn of the knot is locked to the preceding half turn

In the photo the locked snake knot is on then left and the unlocked is on the right

Fold a cord in half and bring the upper strand in a half turn around the lower strand

Flip this upside down

Bring the new upper strand down under . . . .

. . . and up through the first bight. Pull tight If you repeat steps 1 - 3 you will get a unlocked snake knot

Take the upper strand and bring it down under and back up through the bight and pull tight

Flip the knot upside down and bring the upper strand down under and up through the bight

and again . flip knot, and bring upper strand around

and again

and again. Repeat until you reach desired length