Hamsters are the guinea pigs of pets

Hamsters are the guinea pigs of pets

This joke is a pun centered around the use of the word "guinea pig". Guinea pig can mean a specific animal of the species Cavia porcellus, but the word can also be used to denote that something is a test subject (because guinea pigs are traditionally used in animal testing in laboratory settings.)

The phrase "A is the B of C" means if you were to take object A from category C, and compare it to an object in a different category it would be the most like object B. For instance: "Parmesan is the Mercedes-Benz of cheeses", which means that if Parmesan cheese were a car, it would be a Mercedes-Benz, since it is excellent.

So, given those things the joke could mean (if you use the word guinea pig colloquially as a test subject) "people get hamsters because they want to test out the idea of having a pet". This is something that actually does happen - I myself have told kids that if they want to test out what having a pet is like they can have a small fish, and if they can take care of it then they can have a dog.

But, if guinea pig is used literally then this joke could also mean "If a hamster were a pet it would be a guinea pig". That is funny is because a hamster is a pet already, so if it were a pet it would be a hamster.

Now, hamsters and a guinea pig are both small rodents that people often get as first pets, and people often even use the names interchangeably and/or don't know which is which, so this might also be a play on the fact that they are both very similar in many people's minds.

Anyway - this is an interesting joke, and I found it moderately funny.