Here's a few things I've done recently for Sketch Dailies on Twitter - it's a community that throws out a daily topic that literally thousands of artists take part in. These ones were days when I needed to clear the cobwebs out of my head to focus better on things that I'd been working on. I wouldn't call these sketches really but more experimentations/exercises. The topics were "Three Blind Mice", "Jackalope" & "Selfie".