Math for Heaven's sake

In response to this entry at the Curt Jester, Brendan responded with this:

Which reminds me. . . .
. . . .after the waters had subsided, and the Ark came to rest, the doors were opened, and Noah said to all the animals: "Go forth and multiply".

All the animals left the Ark; but then Noah saw that two snakes were still inside.

"I said to go forth and multiply", said Noah; and they replied:

"We can't - we're adders."