Guinea Pig — behavior & socialization (communication, body language, social needs)

Source: first-hand owner-practical care pages, saved to source_file; every claim below is a C1 byte-substring of it.

If your guinea pig's behaviour becomes an ongoing problem, or they show signs of stress or fear, ask your vet or clinical animal behaviourist for advice.
Make sure your guinea pig stays happy and healthy, by giving them access to the things they need at all times - including space, food, water, safe hiding places, companion guinea pig(s) and toys.
Social time - guinea pigs are very social and need to interact with other friendly guinea pigs.
Signs a guinea pig may be suffering from stress or fear can include:
You should keep your guinea pig with at least one other friendly guinea pig, unless you're advised otherwise by a vet or clinical animal behaviourist.
Tunnels - guinea pigs like to tunnel, so make sure they have suitable materials that allow tunnelling behaviour, such as pipes and deep areas of hay.
If it changes, it could be a sign your guinea pig is distressed, bored, ill or injured.
As a guinea pig owner, you'll need to keep a close eye on your pet's behaviour.
A guinea pig's behaviour depends on its age, personality and past experiences.
These behaviours are often a sign that your pet is unhappy.
Pets can develop a range of behaviour problems.

Source: pdf-raw/owner-care/guinea_behavior_combined.txt · RSPCA pet care advice (rspca.org.uk)

Sources