Wow!

A radio telescope in Ohio recorded 72 seconds of a strong narrow signal from Sagittarius, and the astronomer who found it on the printout three days later wrote one word in the margin.

Nothing like it has ever been heard again, from that patch of sky or anywhere else, despite a great many attempts. The telescope's design meant it saw each point twice, about three minutes apart, and the second look found nothing — which is odd, and has never been explained.