Rebirth - Imagine the process of rebirth is like a flowing river, every moment it is the same river and yet it is different. As we travel through lifetimes, we are propelled by the causes we have done this life into the next. So in every life, we are still the same river.... but yet we are different. Each lifetime whether as a human or not, has lessons for us to learn in order for us to evolve spiritually...
Each realm of rebirths have the causes or reasons: Heaven - benevolence, Hell - Hatred, wickedness and Anger, Demigods ( asuras ) Benevolence but stained with Jealousy and hot-temper, Humans to evolve spiritually, Animals due to extreme lust, greed and ignorance and last but not least Hungry Ghosts ( Pretas ) - extreme miserliness and meaness.
There are of course quite a few more attributes associated with each realm, Buddhists aim to get OUT of that rebirth cycle that only leads to suffering.
Say for example, I am someone who has caused the deaths of millions and therefore created extremely negative karma. Each and every pain or suffering I have caused would be reflected upon what I become in my next lifetime.... THIS is what some teachers say hell is.
But since everyone is not extreme in wickedness and evil, assuming I have caused many deaths with malicious intent, but I am also a person who saves a lot of lives, creating opportunities for poverty stricken kids to have education.... If I were so fortunate as to take rebirth as a human being, I would be born in a land stricken by the suffering I have caused, my phyiscal self will most likely be full of pain and diseases I have caused others in the past but with a brilliant mind that is able to learn fast.
THAT, is just the surface of Buddha's doctrine in rebirths. As you investigate further into the reality of karma, its causes, its effects and even its branch or dormant effects, you will see that each facet in our very lives is karmically linked, and will propel us towards the future lifetime, its possibilities are virtually fathomless and endless!
The Buddhist idea of Heaven and Hell is not based on a Judge, Jury and Executioner deity as in Christianity, Buddha taught that whatever benevolence or malevolence we have created or caused or even caused others to cause will determine if we merit heaven or hell. The idea here is, we can fool anyone and everyone, but we cannot fool our inner mind, where which every thought, attitude, motivation, word and emotion has been recorded in our Consciousness which is like an unerasable hard disk. In others words, if we were horrible people... our minds will know, its "PAYBACK" time... and will take on a rebirth MOST appropriate to our previous attitudes, thoughts and habits...
Here is something for you to note: Next time you are out eating look around at people, some will fork the food into their mouths, while Others... will bring their mouths closer to the plate so that the fork hardly leaves the plate.... In scene 2, do you find a similarity between that eating style and a doggy or kitty's eating habits? So there is a possibility that person could have been an animal in his/her past life... and such "habits" are hard to shake, so they leave such hints as reminders.
p/s: you can only take rebirth as something with sentience, so it is doubtful that you will ever take rebirth as a bottle of beer or a plasma TV