These secretions are neither truly solid, like a cement, nor fluid, like the water under a sucker. They are visco-elastic gels, usually based on mucus. Most people consider viscous gels to be sticky, because that seems intuitively reasonable. Nevertheless, mucus is typically used as a lubricant. Marine animals are almost invariably coated with a slippery mucus.
Mammals use slippery mucus to line their digestive, respiratory, and reproductive tracts.
It is impressive that limpets can convert a slippery gel into a powerful adhesive. My research plan is to understand the biochemical changes that trigger this change in mechanical properties. I have identified two specific changes involved in the conversion of slippery mucus to adhesive mucus. I am currently attempting to purify the 118 kD protein with the goal of characterizing it. Using biochemical and molecular techniques, I hope to gain enough information about this protein to predict how it increases the adhesiveness of mucus.