Possible Clues:

• Slick goo
• Gooey seeping stuff
• Catfish coating
• Algae, e.g.
• It might ooze
• Slippery mud; slug trail
• Nickelodeon-style gunk
• Trail behind a slug
• Goo made at home with glue, food coloring, and saline solution
• Viscous goo