A reflex.
Peristalsis is the term for the rhythmic contractions of the esophagus. These wavelike contractions move food toward the stomach.
Electrical stimulation of the brain. DBS.
Electrical nerve stimulation
The tendon that connects the hamstring to the knee is called the patellar tendon.
WHAT IS THE ANSWER ISN'T IT CALLED "ANSWERS" GIMME THE ANSWER
only in the last trimester when they prepare the uterus for labor and are called Braxton Hicks contractions.
a spasm
the heart
peristalsis
I think you may be referring to what are called "Braxton-Hicks" contractions.
Tapping on the patellar tendon stretches receptors called the muscle spindles in the quadriceps muscle group of the anterior thigh. This stimulus evokes a rapid motor reflex to contract the quadriceps and shorten the muscles. This process is called the patellar reflex.
Oral sexual stimulation for a man is commonly referred to as fellatio or a blowjob.