A fierce curse is directed at the wicked, expressing a deep wish for their gradual decay and complete disappearance from the world. Vivid imagery drawn from nature and human life paints a picture of those who do evil slowly fading away.
The primary approach among commentators compares the wicked to a snail. As a snail moves, it leaves a trail of slime, making it appear as though it is melting and shrinking with every step. The hope is that the enemy will slowly waste away, losing their life force and dissolving just like a moving snail, or like a snail drying up when the sun beats down on it [רש״י, רד״ק, מאירי, שטיינזלץ, מצודת דוד, מלבי״ם]. Alternatively, this melting comparison might refer to a fish or creature that dissolves in its watery environment, or even a fleeting stream that simply flows away and vanishes [רש״י, אבן עזרא].
The desire for the wicked to remain in darkness is further illustrated through two main ideas. The first explains the imagery as a prematurely miscarried infant, a tragic loss that falls before its time and never gets to see the light of the sun [רש״י, אבן עזרא, רד״ק, מאירי, שטיינזלץ, מצודת דוד]. The second perspective describes an animal that lives underground, such as a mole, which is born without eyes and spends its entire existence in total darkness, forever hidden from the sun [תורה תמימה, רש״י, מאירי, מלבי״ם]. A unique variation of this idea suggests a blind species of snake that turns hard as a stone and crumbles to pieces when touched [מלבי״ם].
The shared theme connecting the snail hidden within its shell, the miscarried child, and the blind mole is a life trapped in darkness, completely cut off from the sun [רד״ק]. On a symbolic level, the sun stands for the light of salvation, a dawn that the wicked will never be allowed to witness [מצודת דוד].
Taking a different path, the imagery can be understood through the historical struggle of King Saul and his followers hunting down David. In this reading, it is actually David who felt he was melting away from the terrifying fear of death, feeling like an unborn child who would never see the sun. The wicked men hunting him are compared to the moon attempting to rise up and boast over the sun. They face punishment because they failed to observe the sun and learn from its quiet humility. Instead of embracing modesty, they chose arrogance, actively trying to destroy David's rightful kingship [אלשיך].