What do the sexual terms "lemonsqueeze" and "cowbell" mean?

Must be 18+: The sexual term “Lemon Squeeze” has a few different meanings:

The most agreed upon is “the act of squeezing and rotating a woman’s breast clockwise, then counter-clockwise.”

Robert Plant, from Led Zeppelin implies that it refers to squeezing a man's testicle(s). In the song Travelling Riverside Blues he sings the lyrics:

• Squeeze my lemon 'till the juice runs down my leg-a
  Squeeze it so hard, I'll fall right outta bed
  Will you squeeze my lemon 'till the juice runs down my leg
  I wonder if you know what I'm talkin' about
  Ah, well, the way that you squeeze it, girl-a
  I swear, I'm gonna fall right outta bed

The sexualized version of "cowbell" describes a man swinging his scrotum between a woman’s breasts, bouncing off of each one like the clapper of a cowbell.

One of the first written documents to illustrate alternative sexual positions was The Kama Sutra by Vatsyayana. It is estimated to be 1,500-2,000 years old.