Though most bees fill their days visiting flowers and collecting pollen, some bees take advantage of the hard work of others. These thieving bees sneak into the nest of an unsuspecting "normal" bee (known as the host), lay an egg near the pollen mass being gathered by the host bee for her own offspring, and then sneak back out. When the egg of the thief hatches, it kills the host's offspring and then eats the pollen meant for its victim. Sometimes called brood parasites, these bees are also referred to as cuckoo bees, because they are similar to cuckoo birds, which lay an egg in the nest of another bird and leave it for that bird to raise. They are more technically called cleptoparasites. Clepto means "thief" in Greek, and the term cleptoparasite refers specifically to an organism that lives off another by stealing its food. In this case the cleptoparasite feeds on the host' hard-earned pollen stores.

Humans usually experience sound as the result of vibrations in air or water. Although sound that humans can sense is usually carried through these media, vibrations can also travel through soil, including rocks. Thus, sound can travel through a variety of substances with different densities, and the physical characteristics of the medium through which the sound travels have a major influence on how the sound can be used. For instance, it requires more energy to make water vibrate than to vibrate air, and it requires a great deal of energy to make soil vibrate. Thus, the use of vibrations in communication depends on the ability of the sender to make a substance vibrate. Because of this, large animals such as elephants are more likely than small animals to use vibrations in the soil for communication. In addition, the speed at which sound travels depends on the density of the medium which it is traveling through.

The repairman is called in when the smooth operation of our world has been disrupted, and at such moments our dependence on things normally taken for granted (for example, a toilet that flushes) is brought to vivid awareness. For this very reason, the repairman's presence may make the narcissist uncomfortable. The problem isn't so much that he is dirty or the job is messy. Rather, he seems to pose a challenge to our self-understanding that is somehow fundamental. We're not as free and independent as we thought. Street-level work that disrupts the infrastructure (the sewer system below or the electrical grid above) brings our shared dependence into view. People may inhabit very different worlds even in the same city, according to their wealth or poverty. Yet we all live in the same physical reality, ultimately, and owe a common debt to the world.

Adolescence is a stage of development in which teens have superb cognitive abilities and high rates of learning and memory because they are still riding on the heightened synaptic plasticity of childhood. These abilities give them a distinct advantage over adults, but because they are so primed to learn, they are also extremely vulnerable to learning the wrong things. How does this happen? It is all because the brain wants rewards and anything that is learned, good or bad, that stimulates the production of dopamine is interpreted by the brain as a reward. This means a little bit of stimulation to a teenage brain whose synapses are firing all over the place leads to wanting more stimulation that can, in certain situations, result in a kind of overlearning. The more commonly known name for this overlearning is addiction.