Here are the possible solutions for they go up and down but not side to side clue
Answer
Clue
Relevancy
nods
Clue
They go up and down but not side to side
Definition
NOD, to give a quick forward motion of the head
longu
Clue
Feature of "butte" but not "but"
seance
Clue
Activity in which people talk to the dead (but not really) (but maybe)
coral
Clue
Creatures that can't move but have sex by constantly and simultaneously ejaculating on a full moon once a year. It's called "broadcast spawning" and there are videos and they are glorious
Definition
a mass of marine animal skeletons
atms
Clue
They're known for 10s and 20s, but not 30s
eels
Clue
Some are electric (and these are not technically of the namesake order, but that's what they're called, so let it go)
Definition
EEL, a snakelike fish
weeble
Clue
Toy advertised with the slogan "but they don't fall down"