Before revision: Additionally they feature very tight passages from one tunnel to a lower tunnel called "Schlupf" (slip out) that is too narrow for older or overweight persons – a person needs to crawl under the slip hole, stand up thereby sliding the shoulders through the skin-tight hole, allowing to crawl onto the higher tunnel.
After revision: Additionally they feature very tight passages connecting one tunnel to a lower tunnel called a (slip out) , which are typically extremely narrow and impassable for some, as crawling under the slip hole, and then standing up to slide the shoulders through the ,, is necessary to crawl into higher tunnel.