混成体の培養

Returning Krasis Incubation to its owner's hand is part of the cost to activate its last ability. Once that ability is announced, players can't respond to it until after you've paid its activation cost and returned Krasis Incubation to hand.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.