Here are some collective nouns for groups of animals:

alligator congregation

cheetah coalition

cougar schoolyard

eagle convocation

goose gaggle

lark exaltation

owl parliament

Is it in behalf of or on behalf of?

The Merriam-Webster online dictionary has the following:

A body of opinion favors in with the “interest, benefit” sense of behalf and on with the “support, defense” sense. This distinction has been observed by some writers but overall has never had a sound basis in actual usage. In current British use, on behalf (of) has replaced in behalf (of); both are still used in American English, but the distinction is frequently not observed.

in behalf of means for the benefit of
The letter was written in behalf of a colleague
The money was collected in behalf of hurricane victims.

on behalf of means as the agent of
The lawyer acted on behalf of her client.
The producer accepted the award on behalf of the cast.

Cut to the chase means get to the point or the exciting part. It comes from movies with a chase scene preceded by less interesting material.

catercorner (kittycorner) means not directly across from something

catawampus (cattywampus) means crooked

under the table means secretly
The payment was made under the table.

above board means open, honest, legal
The transaction was completely above board.

These words appear to come from passing money below a table  (secretly) or above a table (openly).

not the brightest bulb in the box means someone is less intelligent

Here are a few of the more than 100 I found:
elevator doesn’t go all the way to the top floor
the lights are on but nobody is home
not the sharpest knife in the drawer
a few cards short of a full deck

to be let off the hook means to be relieved of an obligation
Without any evidence, the police had to let the suspect off the hook

It likely comes from having a fish on a hook and releasing it.

off-the-cuff remark means without prior preparation
He made a few off-the-cuff remarks when he received the award.

It refers to speaking from notes written in haste on one’s shirt cuffs.

out of hand has at least two meanings:

out of hand means without thought or consideration
He dismissed the suggestion out of hand.

out of hand means not under control
The crowd was getting out of control.