I found the following on chimeras:

http://en.wikipedia.org/wiki/Chimera_(genetics)

Apparently there are a lot of different type. Mixed species might be the original mythological kind but what might be happening in ball pythons would be more like reverse twinning. Instead of one fertilized egg splitting into two genetically identical twins, two fertilized eggs merge into one baby. But this paradox ivory may be one of the other scenarios mentioned where two sperm fertilize one egg but interesting that the male's genetic material could overlap to create ivory if that is the case.