Using the feTurbulence and feDisplacementMap filters, Scott Turner make his SVG line-drawings look like they’re pencil-on-paper-like drawings:
See the Pen SVG Pencil Filter #1 by Scott Turner (@srt19170) on CodePen.
Creating a Pencil Effect in SVG →
💡 If you constantly randomize the turbulence you can create squiggles using SVG or even recreate a heat shimmer effect with SVG