Doh!

The fellows who dined with me told me that jungle fern always exudes black slime. Of course, they were the same people who made sure that everything we ordered was well doused with belacan, knowing how much I enjoyed it. I guess in their case they were being quite accurate when they said that it always secretes black slime because they always ordered it with belacan.

Indeed, several days prior, I had specifically ordered my jungle fern without belacan and the color of the slime was considerably more brown than black.