I found out right away why most mouth artists are painters, because when I tried to use a pencil, I could barely make a visible mark, even with a 4B lead. It was almost impossible to put enough pressure on the pencil without losing control of the line entirely.
A Sharpie might do the job, but rather than breathe too many of those nasty ink fumes (& potentially do more harm to my brain than good!) I decided to try using my Pentel Pocket Brushpen, along with some diluted purply-brownish ink applied with a Chinese bamboo brush.
Another unexpected challenge: it was hard to focus clearly on what I was doing when my face was so close to the paper. I suspect most mouth artists use long brushes for this reason-- some, like Ben Nevis, use special rigs to extend the brush. I had to stop & sit back frequently to make sure the marks I was making weren't completely off-target. I think it would probably be better to work a little larger too, to minimize wobble issues.
Silliest unexpected challenge: drool! Several times I came close to an unintended bleed wash. :-P°°° Afterward I realized that most people do mouth painting with an easel, which would help a lot. Would probably save on neck pain too. If I ever try this again I'll definitely tweak my technique.
Ink on paper, ~5"x4.5"
p.s. I'd planned something completely different to mark the 150th oddment, but once again time did not permit. :-( Still, this is Oddments & Curiosities' sesquicentoddical!
p.p.s. Ces, before you issue any more challenges, I must preemptively state that this is the one & only orifice I will offer to my Oddbody exercises!
Edit: If you haven't seen Ted's contribution (hinted at below) to my virtual Oddbody toolbox, please have a look at the Shut-Eye post!