The bare minimim needed to pat the dog to stop a reset. If the MCU does not do its job it is bitten (reset).

d1m_slog_minimum_watchdog.ino

#include <Wire.h>

void setup() {
  Wire.begin(); // join i2c bus (address optional for master)
}

void loop() {
  Wire.beginTransmission(8); // transmit to device #8
  Wire.write('P');           // sends a char
  Wire.write(0);             // sends one byte
  Wire.endTransmission();
  delay(10000);
}