I guess things get swallowed all the time, but this tale (from a hospital case study in Devon, in Britain) tells us something extraordinary about felt-tip pens. (If you look at this woman's stomach, there's a pen in there near the top.)
It's called "An incidental finding of a gastric foreign body 25 years after ingestion," by Oliver Richard Waters, Tawfique Daneshmend, Tarek Shirazi, in BMJ Case Reports from 2011.
Here's the full report: