Lead poisoning
The human variety of lead poisoning (popular amongst swans) can most easily be caught from the graphite in pencils. Once you have caught lead poisoning (chemical symbol Pb) from graphite (an allotrope of Carbon, C), you can trace your imminent demise by looking at your veins, which will turn black.
When this black, poisoned blood reaches your heart, you will die. The only way to slow this process down, so that you can run home and tell your parents that you're sorry that the last thing you said to them this morning was "I hate school, and I hate YOU", is by pressing one finger over the poisoned vein, which will temporarily 'pause' your circulatory system.
Once you have made your peace with the world, let go, and accept the inevitable.
written by Jo* Bl*th, approved by Log