Forget “the dog ate my homework”, there’s a far more deadly excuse poor students use to mask poor performance, according to Australian celebrity scientist Dr Karl Kruszelnicki.

The dead grandmother index was revealed by Dr Karl during a Great Moments in Science presentation at the Convention Centre for the World Science Festival Brisbane.

Students trying to escape an exam often use the excuse of a death in the family and grandmothers are usually the first to be killed off, according to Dr Karl.

He presented statistics that showed when it came to final exams, for every 100 A-Grade students, nine dead grannies were reported compared with 100 F-Grade students who apparently lost 218 grandmothers in the exam period.

As well as dead grannies, the presentation dealt with cats escaping death.

According to Dr Karl, a cat has a better chance of surviving a 32-storey fall than a seven-storey fall.

As the cat falls, it is still accelerating until it descends more than seven storeys.

At that point the cat begins to react to the situation and adjusts its body position in the air to ensure that every part of its body hits the ground at the same time and therefore has the highest chance of survival.

Dr Karl said, however, the case was not the same for dogs.

A full report on Dr Karl’s presentation can been seen by clicking HERE.