Pretensions is a word given to those who claim to be something that perhaps they really are not. It is a little like the word pretend. The word comes from the word 'pretend'.
A silkworm is the caterpillar of the Silkworm Moth which spins a cocoon that can be processed to give silk fiber, silkworms is the plural.
Guinea pigs are tailless animals, slightly similar to rabbits, and are kept in hutches as pets just like domestic rabbits. The name guinea pig can also be given to someone who is being used for an experiment.