Hm, I can still switch between the crack and cigar, much like I can switch between the duck and bunny. And with the same ‘trick’; it depends on where I look. If I focus on the back-of-the-head/nose I see the bunny. If I focus on the ears/beak I see the duck. If I focus on the ash/pebble I can still see the crack between the stones, it’s only when I focus on the other side, that’s wedged into the wall that i see the cigar.
I’ve always been pretty good at those 3-D magic eye pictures as well. Maybe it’s a skill.