At the beginning of the computer memory there is a list of all the files with their names, locations and sizes. When you delete a file the record of that file is deleted from the list. From now on the place in the memory with that file’s information is considered free and can be eventually allocated for a new file. For this reason it is possible to “undelete” files within some time period after deleting them - right up to the moment when the data gets actually overwritten, which may be a while.

Nothing stops you from setting whatever price you want, unless you are a monopolist or coming close. In that case there are anti-monopoly laws which are meant to prevent this from happening.

The machine in the airport only scans things inside it, it doesn’t leak X-rays outside. In hospital the entire room with the patient is the machine. The reason for this is that it’s not possible to remove a part of a human body, put it in the scanner and then put it back on the body. And full body X-rays would be excessive and unnecessarily dangerous. So they only shoot X-rays through the specific body part in interest while the patient is in the room.

A shaman in tribal societies of Northern Eurasia is a person who can communicate with the spirit world in order to make the spirits help people in desired ways: healing, fortune telling, enchanting amulets etc. A shaman is supposed to enter an altered consciousness state to do this. For that they can take certain mushrooms or other substances, meditate, make hypnotizing music and dances and so on. In short, a shaman in a shamanistic belief system is like a priest in a religious system.

Liquid water evaporates at all temperatures, so puddles disappear because they evaporate. The evaporation is somewhat faster with higher temperatures and slower with lower temperatures. Evaporation happens from the open surface of water. The larger the surface, the faster the evaporation. For this reason a puddle evaporates faster than the same volume of water in a glass. Boiling, however, happens throughout the entire volume of water at the same time, and is therefore much faster than simple evaporation.

I’ll try to go for a true ELI5 here. Life needs oxygen to burn food. Burning food gives living organisms a lot of energy, which they can use to move around, or grow fast, or break up some more food etc. it’s not strictly necessary though, life started out without oxygen, and there are many living things (bacteria and others) today that make do without it. There are other ways to get energy, doing it with oxygen is just much more effective. Organisms like us can’t live without oxygen because we came to rely on it.

Music is similar to the patterns of speech, and speech contains tonal cues (prosody) which reflect the emotions of the speaker. Figuring out other people’s emotions is very important for us, so we are primed to hear and discern these prosodies in speech, and, as a side effect, also in music. And discerning other people’s emotions involves feeling the same emotions ourselves (empathy). Therefore music makes us feel emotions.

All celestial events occur in cycles, so whenever a cycle is complete, the same events occur again. In case of solar eclipses, the cycle is about 18 years (called a “saros”). This is a period of time in which the Moon and the Sun both complete whole numbers of their own cycles, setting them to repeat the same events all over again.