It's an old jazz tune by Dizzy Gillespie...lyrics are phish though (go figure haha)
There is a theme of STD's and using protection in the album, especially in the song "Cavern." Manteca is Spanish for cooking lard, I would guess with a reference to a curvy woman, too.
In "Cavern," we're reminded to take care of our shoe after a list of synonyms for condoms. Here, the singer laments a "Crab" in our "Shoemouth."
Elsewhere in the album, the singer can no longer carry on his relationship with his lover due to being in the hospital with a "tube" in his "ween."
Not the most mature way to address the AIDS epidemic that was raging at the time this album came out, but as a teenager when this came out, I got the message. It's a regular PSA!
From my Guelah Papyrus comment:
I think this song is about expecting to catch a cheating girlfriend in the act, with undertones of fears of venereal disease as a running theme? Why? Well, when you listen to the other lyrics on the album, STD's are something of a running theme-- it's a public health announcement to jam band types everywhere. "Whatever you do, take care of your shoe" (Cavern) lest you get a "Crab" in your "Shoemouth" (Manteca)
"In summing up, the moral seems A little bit obscure...
Give the director a serpent deflector A mudrat detector, a ribbon reflector A cushion convector, a pitcher of nectar * A viral dissector,a hormone collector"
(Cavern) - this entire list is a collection of synonyms for condoms. With the exception of a "picture of Nectar." Nectar's was a club that Phish played in and while I haven't seen the proprietor myself, it would presumably be enough of a turn off to prevent any activity that might result in catching anything!!! And I think bacteria can come in the shape of little serpents, ribbons, rods, or tiny spheres. Yuck.
This album came out during the AIDS epidemic when I was a teenager-- I think the message was pretty clear at the time. The remainder of "Cavern's" lyrics contain a lot of disease imagery, and other earlier tunes like Golgi Apparatus suggest that microbiology tends to come up in Phish lyrics.
So the singer imagines himself paralyzed by a spider, a "fly on the wall" to witness the tryst of his lover, and then imagines walking in, causing frowns all around-- and noticing that his photo frame on the nightstand has been turned flat on the table.