The harp and the shamrock are both symbols of Ireland. Often confused with four-leaf clover, the shamrock has three leaves which, legend has it, St Patrick used to illustrate the doctrine of the Holy Trinity. The Celtic harp or Cláirseach has a distinctive shape familiar to drinkers of Guinness beer. In Celtic Ireland and Scotland, harp players were important members of society, respected for their musical and storytelling abilities.
Similarly, the lion and unicorn are symbols of England and Scotland respectively. The origin of the three lions, now seen on England football shirts, lies in the Norman Conquest, when England adopted the arms of the House of Normandy: two lions rampant on a red field. During Richard The Lionheart's reign the arms changed to three lions passant, though the reason for this is unclear; the third lion might represent Richard himself.
When England and Scotland were united under the Scottish King James VI & I he added a Scottish unicorn to the royal coat of arms. According to myth a free unicorn is extremely dangerous, so in the coat of arms it is chained up.