Which mechanism do sponges possess that makes a predator think twice before attacking it?

Sponges come under phylum Porifera. They exhibit cellular levels of body organization and are inactive in nature. The sponges are known to generate and discharge some kind of toxins. The discharging of the toxins may perform various activities like shielding themselves against the parasites and predators. However, these toxins are also considered to harm other sponges.  

This mechanism of sponges makes a predator think two times before attacking it. The sponge will generate toxins, which could disorder the metabolism of any species that try to eat them. However, the majority of the predators possess the tendency to detect the toxin via their sense of smell, and thus, helps them in avoiding the sponges.