Pull the start of the straight-edge cut piece loose, so that its end becomes fluffy.
Straightening

Straighten the part you are working with, using a curler, styling tongs or an iron (on the 'wool' setting), until it has a slight wave.

Straighten the part you are working with, using a curler, styling tongs or an iron (on the 'wool' setting), until it has a slight wave. Do not pull it too hard, so the braid remains intact.
Pull gently to the right length

Now make the piece that you are working with longer and looser: run it through your hands and pull it gently bit by bit in the lengthwise direction, but so that the piece still remains intact.

If you want, you can mix the tuft with Wool Crepe of another colour.