hi there...I got my first Dumeril's Boa back in December (adult male) and mine has a spot on the chin too...I guess that's normal for them, but since I don't have much experience with these guys, maybe someone else can verify that.
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-David
Check out my pet pics at:
http://www.myspace.com/obx_fisherman
1.0 ball python (Pandora - don't ask)
1.0 argentine boa (Prometheus)
0.1 hogg island boa (Andromeda)
0.0.1 brazilian rainbow boa (Inara)
1.0 kenyan sand boa (Diablo)
1.0 normal corn snake(Cypress)
0.1 amel. corn snake (Morgan LaFay) RIP 
0.0.2 baby corns (Romulus and Remus)
- 1 normal, 1 ghost
0.0.1 banded cali. kingsnake (Cain)
1.0 tangerine honduran milksnake (Narcissus)
0.0.1 snow corn snake (Valkyrie)
1.0 amazon tree boa (Pegasus)
1.0 colombian boa (Athena, for now)
0.1 albino san diego gopher snake (maybe Octavian)
0.0.1 sandfish skink (Slick)
0.0.1 fire skink (Phoenix)
1.0 dog (Luke)
the wife's pets:
1.0 bearded dragon (Leonidas)
1.1 ferrets (Ares, Enyo)
1.2 cats (Galahad, Ripley and Sassy)
0.1 Boxer (Zoe)
2.0 rats
NEWEST ADDITIONS:
1.0 adult Dumeril's boa (maybe Hannibal)
0.0.1 baby yellow amazon tree boa (affectionately called
Snuggles)
