The Arecibo response is a mysterious crop circle which appeared in farmland next to the Chilbolton radio telescope, apparently in response to the famous Arecibo message which was sent into space in 1974  from the Arecibo radio telescope in Puerto Rico.
The response message itself differs substantially from the original Aricebo message. The 1974 transmission contained binary encoded information about our base-ten number system, organic elements needed for life on earth, formulae for sugars & bases found in human DNA, the number of base-pairs in DNA, the structure of DNA, a simplified representation of a human being, the average height of a human, the population of earth (in 1974), our solar system (indicating earth as a raised third planet relative to the system), a representation of the Aricebo telescope as well as the diameter of the telescope itself. 
- The number system is indicated as base-ten, just like the original message.
- The atomic numbers for life is almost the same, except silicon has been inserted between oxygen and phosphorous.
- A new set of nucleic formulae is included, some of which appear to be derived from silicon.
- A new value in base-pair amount, indicating more base-pair sequences (roughly 4,294,966,110 bp's).
- The structure of the DNA has been changed, indicating an additional strand to our own.
- A simplified representation of the intended sendee. Indicates a larger head, as well as more pronounced set of eyes.
- Average height of the intended sendee is drastically less than that of the average human. It comes out to about 3'4.
- The population of the intended sendee has been changed to reflect a much larger population to our own: 12.7 billion. This may or may not be a population value taken in 1974, or of that in 2001.
- The visual representation of the solar system has changed. The intended sendee's sun is smaller in size to our own. Not only this, but three planets are highlighted instead of the one planet (Earth) indicated in the first message. In the response message planets three, four and five are highlighted, with an extra emphasis on the fifth planet. There are also nine planets in the response message, just like our own, however it is purely speculative as to why this is so.
- The "communication device" has changed. Instead it depicts a crop circle that also appeared near Chilbolton observatory in 2000.
- The diameter of the "communication" device is changed. The new diameter is now 2789.52'.
- Note, The Aricebo message was also sent to the stars with the Cosmic Call transmissions in 1999 and 2003. Wikipedia link. https://en.wikipedia.org/wiki/Cosmic_Call
Not far from that message, another crop cicle formed just before the Chilbolton response. This formation forms what could be described as a humanoid face generated from a series of dots which create a contrasting effect. So far, nobody has attempted to repeat the Aricebo resonse at Chilbolton observatory.
James Deardorff, former Senior Scientist at the National Center for Atmospheric Research, in Boulder, Colorado, has attempted to calculate the Arecibo response to be less than two chances out of 10 billion to be a hoax.