Phrase: "goes like a rattlesnake"?
The intended expression here is probably:
shag like a rattlesnake:
To copulate energically.
Sex-Lexis.com
The corresponding expression used outside BrE is "fucks like a rattlesnake", although I was able to find another example which tones down the language:
Ya wanna go to Meeka, Doug? Plenty of yorgas up there, mate. Meekatharra womans rock like a rattlesnake, unna, Floyd?
Day of Dog
(The above is a 1981 quote found in the OED. The speaker is likely Australian aboriginal.)
See also the definition in A Dictionary of Slang and Unconventional English.