Acid Spray (Morph of Arrow Spray) is incorrectly using spell crit instead of weapon crit. Someone considered that maybe the game considers "poison" as magic and therefore uses spell crit. Acid Spray is the only "poison" bow ability/morph that does this. Evidence Below:

>>Snipe (Morphs) - this one took some time to do

Test 1: 0% spell crit / 34% weapon crit

(Focused Aim) - "Physical" damage
33 out of 100 were critical hits

(Lethal Arrow) - "Poison" damage
36 out of 100 were critical hits

*results consistent with <weapon crit> as the contributing statistic

>> Poison Arrow (Morphs)

Test 1: 0% spell crit / 34% weapon crit

(Poison Injection) - "Poison" damage
36 out of 100 were critical hits

(Venom Arrow) - "Poison" damage
34 out of 100 were critical hits

*results consistent with <weapon crit> as the contributing statistic

>> Arrow Spray (Morphs)

Test 1: 0% spell crit / 34% weapon crit

(Bombard) - "Physical" damage
35 out of 100 were critical hits

(Acid Spray) - "Poison" damage
0 out of 100 were critical hits

*inconsistent results for Acid Spray, Bombard seems to use <weapon crit> as the contributing statistic

Test 2: (with Magelight): 7% spell crit / 34% weapon crit

(Bombard) - "Physical" damage
38 out of 100 were critical hits

(Acid Spray) - "Poison" damage
8 out of 100 were critical hits

*results consistent with <spell crit> as the contributing statistic for Acid Spray

CONCLUSION: Acid Spray is the only "poison" weapon ability that uses spell critical as a contributing statistic instead of weapon critical. If "poison damage" was intended to be "magic" and therefore use spell crit, these results show inconsistency with that logic.