Here's why:
* Terrestrial means "relating to the land" and all the organisms in this chain live on land.
* Food chain refers to the sequence of organisms where each organism eats the one before it.
In this case:
* Field mouse eats plants (primary consumer)
* Fox snake eats field mice (secondary consumer)
* Fox eats fox snakes (tertiary consumer)
This simple food chain demonstrates the flow of energy through a land-based ecosystem.