Mrs. L.A. applied Advantage flea medicine to Tonka and Goo. A little bit later, goo had a six- or seven-inch goocicle handing down from her mouth. She seems OK, and she ate after ‘mom’ wiped her face. I wonder if she somehow got the Advantage in her mouth? (Mrs. L.A. applies it to the back of their necks so they can’t lick it.)
She might have licked Tonka’s med spot? Drooling is one of the symptoms of overdose. Hie thee to the veterinarian!!!
The vet says it sounds like Goo might have had a little taste of the medicine and drooled because it tasted bad. We just need to keep an eye on her. She only dropped once, she ate, she doesn’t appear to be in distress, and she’s snoozing.
ETA: No chance she licked Tonka. They’re not that close yet.
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Just be glad you didn’t name her Exploding Head.
We didn’t name her. 
‘Drooled’.
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Poor Goo. Keep an eye on him.
I am disappointed that the lump under the bedcovers is apparently not cat #3.
Tonka is obviously in great need of a tummy rub in that picture.
Long ago, one of my cats had the same reaction to flea powder. The symptom went away, and I didn’t take him to the vet. A few years later, he had cancer. May have been a coincidence.
BTW, I think I’m in love with Tonka.
So are we. 
Mrs. L.A. was specifically looking for a cat that had been at the shelter the longest, and an older cat that stood a lesser chance of being adopted. Tonka had been at The NOAH Center for six months, and was the longest-term resident there. He’d been in a shelter in Spokane before that, for who-knows-how-long. And he was eight years old. And we were told he’d need sub-Q fluids once a month. And he had asthma. He’s 14 now (24PetWatch says 15), and we’ve never had to give him sub-Q fluids. His asthma is much improved, as he can go days without coughing. He’s flourished in his Forever Home. We love his truncated tail and his fuzzy belly. (But rubbing his belly has earned him the nickname ‘Freddy Krueger’. Most of the time, it’s safe to rub his belly though. Most of the time.) Alas, Tonka’s outside privileges have been revoked. He was down the block the other day, hissing at a neighbour’s feral cats. He wasn’t fighting, and he doesn’t seem to look for trouble; but Mrs. L.A. wants him closer to home. 
As for Goo, apparently the goo-mouth was a one-time thing. She’s quite active today, and we’ve been playing with the ‘bird’ on the ‘cat fishing pole’.
The chemicals (imidacloprid) in that medicine taste bitter and the cat was probably drooling in an attempt to get the taste out of her mouth after accidentally licking it. It is not especially toxic (except to insects!), carcinogenic, mutagenic, or whatever. Imidacloprid is somewhat related to nicotine.