I found this phrase "Taking a line for a walk" in a book I'm reading called The Biology of Art by Desmond Morris, a zoologist with an interest in the ability of some animals to make art.

The phrase seems like the perfect description for what Bella is doing in this video, which is giving me a spontaneous demonstration of how she makes a straight line with a braid that's 6 feet long.  

January of this year was one of seemingly endless creativity on Bella's part.  We got into a mutual encouragement cycle such that each time I photographed a new arrangement Bella would make me another.   The cycle didn't stop until I became exhausted and called it quits -- Bella herself was still going strong.  What a girl!

Enzo is very food motivated and loves chewing bones which is probably why he  chose to use the stuffed bone toys with the rainbow rope toy in these two constructions.   He placed the rope toy and the white bone end to end, creating a broken line which makes me think that he recognized these toys as roughly similar in length and shape.   He ignores the fact that the two objects differ in color and texture, perhaps because the ability of dogs to see colors is limited.
 
Enzo singles out the black bone as different and uses it for variation.   First he places it perpendicular to the rainbow rope toy.   From a human standpoint, the second construction is more advanced because, by placing the black bone parallel to the broken line, it became possible to center the black bone.   This makes the design more balanced and symmetrical.  
 
Young children develop an intuitive knowledge of geometry through play, taking joy in exploring new shapes, patterns, and designs.   In my view, that's what Enzo was doing in this pair of constructions.

My friend Sally is visiting for a couple of days.   She's brought toys for the dogs and they're very excited.   Enzo jumps in her lap and she holds him close, rubbing his back. 
 
They play with the toys for several days before Bella breaks out and incorporates the rainbow rope toy into a construction with lines on either side that appear to recede when I'm looking at Bella through the lens.  
 
Sally is an artist in her own right.   When I show her a pic of Bella's construction she responds, "Yikes --- this is a different sort of artwork.   Kinda like minimalism with very simple bright colors with elegant lines.   I love how she uses the snake.  A gentle zigzag and then a bold curve.  And such perfect alignment."   
 
To me, this construction suggests a sense of perspective, an idea Bella could have gotten from a training session Paul on a set of railroad tracks in the country, where the parallel lines of the tracks appear to recede when you look at the horizon.

 Bella is famous for wrapping herself in the braid toys and Enzo has seen her do it many times.   That's Bella in the first picture with a draped around her shoulders, as if she were a movie sta.
 
Fast forward to New Years Day. I've given the dogs a new braid that's long and thick -- long for more ways to arrange it, thick for playing tug.   Bella begins by rolling around on the braid ecstatically, burying her face in it, then turning belly up so she can toss the braid around with her paws.
 
I'm in the kitchen checking the oven when my husband calls out, "Come see what Enzo's done!   I join my husband in the family room and there's Enzo with this huge braid wrapped around his slender body.   He looks adorable and I grab the camera.   Enzo knows he's done something really great with the new braid because I take 5 pictures of him wearing it!