Softclawjob
When you want to go crabbing on your wedding anniversary because the tides are great, but your wife would rather celebrate your anniversary. So you genetically modify her in her sleep to be part crab, therefor giving reason to go crabbing since she is such a catch. But then you have to wait till she is molting for a hand job, because hard claw jobs are no good.
The silky smooth, yet semi firm gelatinous texture of her softclawjob was enough for me to marry her all over again.