Spanish Fly is an aphrodesiac, iirc. I was looking for a link on this and googled "spanish fly" and this popped up on the first page (maybe already posted, thank you Donjeta for all the updates!!):
Cosby’s history of ‘Spanish Fly’ jokes comes back to haunt him
http://www.msnbc.com/msnbc/cosbys-history-spanish-fly-jokes-comes-back-haunt-him
"In his 1991 appearance alongside King, which was part of a promotional tour for his book “Childhood,” Cosby joked about “Spanish Fly,” which was a slang term in his youth for a pill that could serve as an aphrodisiac.
“Spanish Fly was the thing that all boys from age 11 on up to death — We will still be searching for Spanish Fly,” Cosby told King, who laughed and agreed with him. Then this exchange takes place:
Cosby: And what was the old – the old story was, if you took a little drop – it was on the head of a -
King: Pin.
Cosby: - pin! And you put it in a drink -
King: That’s right. Drop it in her Coca-Cola – It don’t matter.
Cosby: It doesn’t make any difference. And the girl would drink it and -
King: And she’s yours."
(*gross, to think he was making jokes about all of this!! Jmo)