When a cat puts their ears back it means they are scared. A cat with its ears back may act out physically and scratch or bite if approached. Don't attempt to pet a cat further if they suddenly put their ears back while you are petting them. When cats feel intimidated, they fluff up their fur so they seem larger than they actually are to potential challengers. They may even put their tails straight up. These actions mean the cat's fight-or-flight response is engaged. Don't try to touch or approach a cat if they are exhibiting this behavior, as they may bite or scratch you. If a cat rolls over and exposes their belly, this means they feel comfortable being vulnerable with you. You can take this as a sign that the cat is enjoying being petted, as this is submissive behavior. You can continue petting the cat's face or even try petting the cat's back. Listen for purring to confirm that the cat is still enjoying your touch. Even if a cat exposes their belly, that does not mean that they want to have their belly rubbed. Most cats don't enjoy having their stomachs touched, so it is best to avoid this. When cats are sick they will cough, sneeze and may vomit, just like us. If the cat is exhibiting these signs and seems to be hiding in a small space, they may be sick. If the owner is available, let them know so they can contact a veterinarian. Do not attempt to pet this cat. If the cat is a stray, and you are concerned for its wellbeing, contact a local rescue group. They can give your further instruction on how to proceed. Do not try to pick up or pet the cat, as you may put yourself at risk of rabies or a bite.

Summary: Avoid petting a cat with its ears back. Avoid petting a cat if its tail is fluffed and straight up. Reward a cat that rolls over and exposes their belly. Recognize signs of distress or Illness.

Note that each shell lies further and further out from the nucleus of the atom. According to the property of entropy, energy always seeks the lowest possible state of order. The electrons will seek to populate the lowest orbital shells available. When two atoms come together to form a molecule, they seek to use each other's electrons to fill the lowest possible states in the electron orbital shells. Bonding electrons are, essentially the electrons that stick together and fall into the lowest states. Antibonding electrons are the "free" or unbonded electrons that are pushed to higher orbital states. Bonding electrons: By noting how full the orbital shells of each atom are, you can determine how many of the electrons in higher energy states will be able to fill the more stable, lower-energy-state shells of the corresponding atom. These "filling electrons" are referred to as bonding electrons. Antibonding electrons: When the two atoms try to form a molecule by sharing electrons, some electrons will actually be driven to higher-energy-state orbital shells as the lower-energy-state orbital shells are filled up. These electrons are referred to as antibonding electrons.
Summary: Consult a diagram of electron orbital shells. Know the difference between bonding and antibonding orbitals.