Well, the explanation for why animals can suddenly become sentient is as follows:
Above: According to Niel Bohr's model of the atom, atoms are like miniature solar systems complete with 'planets' which we call electrons, and 'suns' that we call nuclei.
The end result is that every animal is like a galaxy - with trillions of planets, each with their sentient civilisations on each one. The proof of it comes from the following:
Above: Studiees by scientists have found that advanced atomic civilisations that live on electrons have been able to create miniature machines (to us, but huge to them) like the above, which we call viruses, but are in fact, planetoid death stars to them.
Above: Some advanced sub-atomic civilisations that reside within animals are so advanced, that they have the ability to shape the entire galaxy (the animal) to becoming sentient, such that the entire 'galaxy' behaves like a body - an extension of themselves. This is not a new concept - it's like the ALZ-113 virus from planet of the apes, which makes apes acquire sentience.
Above: At the end of the day, it's super advanced intelligent civilisations that live on electrons that come together to form a galactic nation, that is responsible for animal sentience.