Yup no problem. You could also teleport to Africa, ReAn all snakes in the desert while flying, extract their poison, and teleport back with 1 liter of poison.
If your opponent is a magus, it's not a poison which will kill him. Any magus can cast a CrCo without fatigue who can give him such high bonus to recovery, and any decent magus has enduring of the berserker to withstand the wound malus. (But maybe that's our saga, where magi have all stamina higher than 0, generally 3 and creo is with rego the most important technique learned (for comparison, I'd say that proportion is : Cr 5, In 3, Mu 1, Pe 2 Re 5).
That's assuming he is at home, because I know of no magus who drinks/eat anything not prepared by himself/sodales in travel, without checking for poison.
If it's a mundane? just teleport him 50 meters high, or in a volcano, or if you are a weak magus, make him sleep during 2minutes and slit his throat. Still no problem. Use a sight version of tunnel if you cannot come close.
Or if you are really weak, just use the CrTe base 1 and use size magnitudes to flood the room with sand, crushing him.
IMS God doesn't care about offspring of animals. If it's planned, it won't happen. In other words, players can try something, it will always fail. That only work when nothing interfere. The cause is not precised, and magi will have no tool to understand it. Yet in other word: stop messing the system which is flawed, and we all know that it isn't perfect. Still, Ars has a way better system than any other games for magic.