Weird phenomena scientists can't explain

All doctors put this effect in doubt but at the same time they can't prove it doesn't exist. One of the most mysterious effects in medicine and science in general is the "placebo effect." It is a miraculous cure of ailment with the help of faith alone. And we are not talking about religious practices, but about self-hypnosis. In other words, a person (hypothetically) can self-heal from some ailment, simply believing in it. All this may sound strange, but as early as the 20th century in a number of countries experiments with people in a state of depression were conducted. The essence of the experiments was that these people were "deceived" by giving them pills instead of antidepressants, claiming that this was new super effective remedy for depression. It's amazing, but the overwhelming majority of people were really healed, thinking that they use real medicines. Despite the fact that today's evidence-based medicine puts serious doubt on the importance of the placebo effect, doctors also fail to prove the absence of it in nature.

Some animals demonstrate striking resistance to cancer.
Cancer is a disease that begins as a result of failure of cellular mechanisms and the formation of "incorrectly working" cells in the body. Not only people are affected by cancer, but also many animals. It is noteworthy that the bigger a living organism is, the higher a chance to develop cancer is. However, there are organisms that are almost completely resistant to this disease, namely, whales and elephants, which completely violate the regularity described above.
Why these animals so rarely suffer from cancer is a puzzle for the whole science. Scientists and doctors have been trying to reveal this secret of nature for several decades, but there are only a few more or less well-formed theories so far. The most optimistic suggests that the secret of elephants and whales is hidden in their genes and evolution itself has made them incredibly resistant to cancer at the genetic level.

Back in the 1860's French surgeon Paul Broca established the relationship between brain hemispheres and hand activity, saying that the hemispheres of the brain and halves of the body are connected cross-wise with each other. However, modern scientists refute such a simple relationship. Back in the 1970's, it was proved that some left-handers had the same left-hemisphere orientation as the right-handers. Scientists from the universities of Oxford, St. Andrews, Bristol and the Max Planck Institute in the Dutch city of Nijmegen have established that the dominance of one of the hands is associated with a group of genes and is being laid at the stage of embryonic development. The study of the genome showed that the PCSK6 gene influences this phenomenon. The definition of orientation depends on the number of mutations, but if the dominant feature is right-handedness, why left-handedness has not disappeared from genetics? Scientists still can't give a single-valued explanation of the phenomenon of left-handed people.

Déjà vu is a state when a person feels that he has already experienced the exact same situation. Scientists make various assumptions of this phenomenon from a change in the coordination of time by the brain to a repetition of the situation from dreams. The scientific research of deja vu is complicated due to the fact that it can't be caused artificially.

Everyone knows yawning is like a disease and it costs one person in a company to yawn, as all the others start to do the same. Scientists also don't know why this happens.
There are many different theories. The most convincing suggests are that the human body perceives the yawning of another person instinctively, as a signal of the body about the lack of oxygen.
The main thing now is not to yawn...