When males' testicles or balls or gonads retract and shrivel. Sometimes due to cold or excitement but primarily in this case due to fear and anxiety.

Like two little turtle heads, connected by skin and sinew, pulling back into its/their shell.

Metaphorically similar to a poo shy turtle but technically, physically and emotionally a very different experience.
She was fun, interesting, sexy and his friends wanted to bone her, but the fact that she was clearly cleverer than him gave him a siamese shy turtle. Would she notice? Would she care if she did? Or, does the fact that even imagining approaching her makes his body eat his balls mean that he'll never have the courage to get close enough for his shriveled sack to matter?

"You know that Bobbitt story, right?"
"Awh, man, don't maaan. Giz me a siamese shy turtle just thinking about it"
by RastaVari October 23, 2013
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