The CA in the tip of the nozzle is reacting with moisture in the small orifice and hardening. Typically once the CA hardens the user will take a pin and stick it down into the nozzle to open it up only to find it clogs up even quicker the next time. What happens is the pin scratches the inside of the nozzle, which allows even more CA to stay in the nozzle causing it to clog up quicker. This process will be repeated several times until the nozzle is no longer able to be used and gets thrown away.
Some companies have claimed to have a clog free nozzle, which in reality is only a very long nozzle that you keep snipping the clogged end off until there is no nozzle left and still end up throwing it away. Other companies simply sell you extra caps and nozzles so you can replace them after they clog.
Mercury Adhesives has actually engineered a nozzle that not only will not clog but has 3 different points of seal to assure the product inside is kept fresh and away from moisture. This cap has a blunt nose, stainless steel pin molded into the cap, which engages into the orifice of the nozzle (not scratching the insides of the bottle) to keep the orifice clean. Inside the tip is a calculated venturie shape, which pulls the CA out of the tip and back into the bottle once the bottle is stood upright. On the very tip of the nozzle is a tapered seat which engages with a tapered boss in the cap creating compression on the tip of the nozzle keeping the nozzle clean and the product inside fresh.
If the cap is replaced each time the user is finished with the product the nozzle will never clog.