During a recent homily a priest told an interesting story of Pope John Paul’s visit to the Baltimore area in 1995:
The Pope was scheduled for a quick trip by the local seminary. But even though it was not scheduled, he wanted to go in and pray at their chapel. So a security team and German Shepherd canine unit that was specially trained to find human beings - using their superior sense of smell, like the ones used after the September 11 attack to find people in the rubble - were sent to search for people hiding in the various rooms.
They searched the halls and rooms and found nothing, and then were sent into the chapel where the Pope intended to pray.
They sniffed in all the aisles and then came to the tabernacle which held the consecrated Hosts. The dogs sniffed and pointed, indicating that they sensed a human being present in the holy tabernacle, and would not leave until their handlers called them off.
This was witnessed by over ten security people.
- From The Wanderer
There's another, longer story, about a host bleeding at the top of the link.