If you check this documentary, you'll see that Borneo natives used blowpipes vs Japanese during 1944-1945. I find this sort of engagement fascinating, since the poison used in the blowpipe dart must have been fast-acting to prevent retaliation by a firearm-wielding soldier. What accounts/sources exist about these skirmishes? What kind of poison was used? What were the outcomes of the skirmishes?
Google's first response provides an answer, that describes the likely toxin. The paper mentions that, "Animals hit by a poison dart, irrespective of the part of the body that is pierced, start to twitch after a few seconds." and, "Reports on dosage specify that 0.3 mg would be lethal for a rabbit. One mg. causes death in dogs (Boer et al. 1999:127), while 0.1mg. is the lethal dosage (L50) per kg. weight for cats (Zahorka 1986:58). The toxicity of [beta]-Antiarin is much higher than that of curare."
I am not a pharmacologist, nor do I play one on the internet. I haven't seen the documentary. With those caveats out of the way.
"Start to twitch after a few seconds" implies that there are (at least) two different models of the blowpipe as a weapon. "a few seconds" is ample time to fire a weapon, if you are aware that you have been attacked. I think it is more likely that the blowpipe wielders were acting from stealth and that the victims were unaware that they had been attacked.
It may be that the victim thought they were attacked by an insect, and were unaware of an attacker; they therefore did not retaliate until the toxic effects had started.
It may be that the victim knew that he had been attacked, but couldn't find the (stealthed) attacker. (I'm also not infantry, but my understanding is that spraying 360 degrees with an automatic weapon is, at a minimum, foolish and wasteful.)
I would like someone to explain why the toxicity for rabbits and dogs is measured as an absolute, while the toxicity for cats is in mg/kg. Which is a better model for humans? Is it possible to deliver 3mg to a human via a blowpipe?
I will focus on the two parts of the question that have not been addressed yet: "What accounts/sources exist about these skirmishes? [...] What were the outcomes of the skirmishes?"
Unfortunately the most substantial account I've found so far is a single paragraph in this article, "The Form of a North Borneo Nativistic Behavior":
On December 17, 1941 the Japanese invaded North Borneo with a force of 25,000 men. Main centers of occupation were established in the Murut area at Tenom, Keningau and Pensiangan. For three years, large patrols of infantry regularly moved from these points through Murut territory, conscripting labor for construction of military airfields, women for army prostitution centers, commandeering rice and other foodstuffs, imposing head taxes, fines and punishing offenders. In late 1943 allied guerrilla agents, parachuting into the area, enlisted Muruts in a force for raids on Japanese patrols and outposts. Re-occupation of North Borneo by the Australian Ninth Division led to heavy fighting through Tenom and Keningau. The 6,000 Japanese stationed in Pensiangan were ordered to stack arms and march 150 miles to the coast at Beaufort. Australian army records show some 400 Japanese reached Beaufort. The remainder were killed by Muruts along the line of march (Tregonning 1958: 221).