Chains

A card chain is when spells and traps are activated in response to a previous activation of spells and traps.

For example, you activate Battlesheeps, and your opponent uses Spell Mine to block the activation, but you use It’s a Trap to block Spell Mine. And so on.

This results in a queue. In Summoned Monsters such queues are solved from the end. That is, the last activated cards activate faster than the cards that were activated at the beginning.

So It’s a Trap will block the activation of Spell Mine which will allow Battlesheeps to activate.