Collective nouns are words used to describe groups of things, often animals. Some examples are:
* A flock of birds
* A herd of cattle
* A pack of wolves
While "barrel" can be used to refer to a container, it doesn't traditionally have a specific association with animals.
If you're looking for a collective noun for a group of animals in a barrel, you could use a more general term like "group", "collection", or "assemblage".
For example:
* "A group of monkeys in a barrel"
* "A collection of hamsters in a barrel"
Ultimately, the best collective noun will depend on the specific context and the types of animals involved.