Caving scares me photo1/2: Getting caught in small spaces underground is a fear of mine. In this photo, my husband is attempting the Sphincter Challenge, which is where you have to squeeze yourself through a hole at a 45 degree upward angle with your feet dangling below you. Most people have to exhale to get through the hole, so for a time your rib cage is compressed against the rock and you have to commit to holding your breath with no air in your lungs to get through it.