Why do your knuckles pop? - Eleanor Nelsen

Important Vocabulary Words From The Video


Synovial is a type of fluid that is found inside the joints. It helps to lubricate and protect the joint.

  • The knee is a joint that is composed of several synovial joints.

Phagocytic is a word that refers to cells that are able to eat other cells. This is a type of cell that is important in the immune system.

  • The phagocytic cells were able to engulf the virus.
  • The phagocytic cells are able to digest the poison.

To fizzle is to give off a lot of gas or smoke, but not to produce any actual flames. When you fizzle a candle, you are trying to make it go out by putting a lot of air into it.

  • The candle fizzed and then went out.
  • The gas stove fizzed and then went out.

Enlarges is a word that is used to describe something that grows or is larger than usual.

  • The company is enlarging its operation, which means that it is hiring more employees.
  • The city is enlarging its boundaries, which means that it is adding more land to the city.

To disprove something is to prove that it is not true. Scientists often use the term to refer to the process of testing a theory or hypothesis to see if it is true.

  • The scientist disproved the theory that the earth was the center of the universe.
  • The scientist disproved the theory that the moon was made out of cheese.

A selfless act is one that is done without any selfish motive. Sometimes people use the word to describe an act of kindness or generosity.

  • She was selfless enough to donate her blood even though she was afraid.
  • He was selfless enough to let me borrow his car.

Weirdly is used to describe something that is very unusual or unexpected. When you say that something is weirdly shaped, you mean that it is not the usual shape for that kind of object.

  • The cake was oddly shaped, with a dome on top.
  • The plant was oddly shaped, with long vines.