Penis captivus (literally "captive penis" in Latin) is a medical term used to describe a rare occurrence during heterosexual sexual intercourse when the female's vagina suddenly clamps down so tightly that the male's penis is unable to be withdrawn for up to several minutes, as a result of a particularly strong vaginismic reflex.
Penis captivus was first described in medical literature in the 19th century, but well-documented accounts by medical professionals have been exceedingly rare. In a 1979 article in the British Medical Journal titled "Penis Captivus - Did it Occur?," a doctor named F. Kräupl Taylor conducted an exhaustive review of medical literature on the condition and found that "almost all the cases mentioned in medical publications and in textbooks are based on hearsay and rumor."
Reasoning that if any case of penis captivus were treated professionally in a hospital, the attending physician would surely have written the case up in an academic article, Taylor concluded that the condition "does not seem to have occurred in the past 100 years or so." But he did find a few very carefully documented instances in the 19th century which he felt "leave no doubt about the reality of this unusual symptom." A German physician named Hildebrandt, for example, writing in 1872, recorded the following account given by a husband subjected to this condition:
He reported that just at the moment when he thought intercourse, which had been quite normal till then, had come to an end, he suddenly felt that he, or rather his glans, was held back deep in the vagina, tightly gripped and imprisoned, while his whole penis was in the vagina. All attempts at withdrawal failed. When he forced the attempts, he caused severe pain to himself and his wife. Bathed in perspiration through agitation, alarm and his failure to free himself, he was finally forced to resign himself to waiting in patience. He could not say how many minutes this lasted, his imprisonment seemed endless. Then — the hindrance vanished on its own; he was free.
But Taylor may have simply overestimated the amount of interest his fellow physicians of the 20th century would take in this condition compared to himself, as several physicians responded to his article by writing of witnessing the condition firsthand. A physician named Brendan Musgrave, for example, published a brief response in the British Medical Journal a few months later, entitled "Penis Captivus Has Occurred," in which he described personally treating a newlywed couple for this condition at the Royal Isle of Wight County Hospital several years earlier by giving the woman an anesthetic. Just to be sure his memory was correct, he called up one of the other doctors present at the time, who replied "I remember it well."
Thus it seems that the condition of penis captivus does occur from time to time even in the present day, but either the parties involved simply wait until the vaginal contraction subsides without seeking hospital treatment, or the treating physicians don't feel it necessary to write up every case in academic-level detail.