A thermistor is a type of resistor whose resistance varies with temperature. In this project, thermistor values are read in through an 'Analog In' pin. The values are then used to control the blinking rate of an LED.
Use a 10k NTC Thermistor. Connect one pin to power (5V) and the other pin to analog pin 2 and to a 1kΩ pull-down resistor.