Local infection rates in nymphal ticks may be low (< 20%) with a low risk of infection (<5%) from a detected, attached tick (most people who get Lyme disease do not notice the tick).

This can happen at any number of places, but in the simplest case the OS is called on every tick of a clock, and decides which process should get the CPU for the next tick of the clock.

Make a list, place boxes next to each item, and tick off the boxes as you get things done.