It is impossible to escape from a Chandelure until it is defeated, and most pokemon are too frightened to flee from a Crobat after meeting its gaze. And yet both of these pokemon pale in comparison to the terror of Ariados, for at least they can be seen and attacked after trapping their prey. Ariados, however, strike from out of nowhere.
The slime which Ariados spit is so thin that they can even strike from the inside of a closed pokeball. The gluey substance can be sent over five hundred feet with precise aim – no small feat for a pokemon of Ariados' small size – and is aimed either at the back of the legs to make turning more difficult, or behind them to create a barrier and cut off the path to retreat.
Trainers must be especially wary when encountering wild Ariados. Ariados slime is illegal in the Pokemon League, because it is impossible to detect when the slime was fired and bench attacks are illegal in standard play. The only rule acknowledged by wild Ariados, however, is the rule of the jungle: kill or be killed. The slime interferes with the ability of a pokemon to return to its pokeball; it can eventually be washed off, but not in a life-or-death battle. Far too many young trainers have lost their first pokemon this way after venturing too far into the Ilex Forest.
It is generally believed that the walls of Fuchsia Gym are made of Ariados slime, and it has been widely rumored that Koga's ascent to the Elite Four involved him using this technique against Agatha to scare her into surrender. (Agatha, protective of her image, maintains that she resigned of her own volition.)