(Psi)SeveredHead
Adventurer
Check the FAQ. Any parts of a summoned creature that are separated from it disappear when the creature does. So poison disappears and does not affect the target if the creature disappears first.
Apparently the Sage disagrees - he said this is possible (even though this goes against the Summoning description).
I've even seen an adventure where a demon summons a weaker demon for food. It would have starved to death over the 5000 years it was trapped if it couldn't do this.