Speeba squints at it.

"...different set of volunteers, same symbols," they direct. Cafly and Awoowoo and Rotheefa line up.

While the volunteers swap around the machine makes a glorpsome noise and generates a new mudball from its glass tank of mysteriously processed mud, depleting it slightly. This second mudball, once dyed, stamped, and fired, splats right on top of the previous one. 

Speeba rolls back and forth, deep in thought, for a few seconds.

Then they say, "All right, same volunteers, same colour, different symbol."

The volunteers attempt this. Orange triangle, anyone?

The launcher fires at a slightly different angle, and the orange triangle mud lands one box to the left, in the bottom left corner box which happens to have two dots in it.

A mechanism at the top of the wall spits two rocks out of concealed holes, which hit square into the other ends of the seesaws and fling Cafly and Awoowoo into the air to land hard but not injuriously on top of the wall.

"Right then." They study the wall. "We know what orange does and what square does and what triangle does. Raclie, Impu, please set yourself on the flingers, and let's try..." They scan the orange row and the square and triangle columns, looking for either a row/column with more has-dots than hasn't-dots cells, or the opportunity to land on a three.

Hrmmmmmmm.

"Try orange star next," they say.

Raclie boops the buttons and pulls the lever.

It splats in the bottom middle and two more Zoombinis get yote.

"Red oval," Speeba says next. Two more Zoombinis bounce and flutter their way onto the flingers.

Fourth column second row, no joy.

So the whole second/red row is a bust. But now Speeba knows where all the columns are. Triangle, square, star, oval, rhombus. And out of all of those, the column likeliest to get hit by an unknown row is...

"Green rhombus?"

Right-hand side, middle row! Now there are 5 people up top and 12 still to go.

So the remaining unknown colours/rows are Blue and Magenta.

"Blue triangle," they suggest. Zoombinis load themselves onto the flinger and make the attempt.

Blue triangle lands right above orange triangle; no joy.