VISUAL differences pythons/boas

I have a very hard to e telling them apart. I know the physiological difference between the two animals but there seems to be very little visually to separate the two. Best I've picked out, boas seem to have a more prominent rounding to the top of their head than pythons, but I pt this idea into action looking through a book and guessing, and the damn emerald boa was mistaken by yours truly for a gtp... haha I'm going to embarrass myself. Any tips?

Typically boas do not have heat pits on their jaws/lips. I say typically bc I think amazon tree boas do...but I'm on my phone and it doesn't always liketosearcg photos for me.

emerald tree boas are more girthy than GTPs. Also, there are more colorations/localities in the GTP line. ETBs have larger teeth, largest of all nonvenomous. I also think the ETBs have more pitbull like heads in my opinion.

yeah ETBs do have heat pits but they look diff IIRC

Yea this is labeled emerald tree boa and those look like big 'ol heat pits. Its so confusing..

http://i53.tinypic.com/2a15jk.jpg

Pic from boas and pythons of the world by mark o'shea.

and here is a GTP
http://s1.hubimg.com/u/1338412_f520.jpg

taken from http://yamanote.hubpages.com/hub/Green-Tree-Pythons

heat pits look diff, eyes look diff, heads look diff ...just takes time i guess to recognize the features

As best as I can tell, Pythons usually have the heat pits and lay eggs, Boas usually don't have heat pits and are live bearers.

often times a boa will "look" softer, a more satin look if you will.. Where as pythons have a "harder" glossier look to them..If you can imagine that..Often times a boas scalation is more granular (smaller) than the pythons..

look at the heads it's a dead give away. boas are more rectangular and pythons are more rounded