It's a mind control agent they transmit in their pheremones.

Mine yowls when they want to go out, going as far as to throw themselves on the floor and claw weakly at the door. Going out will not kill them and I have said as much to them.

It's hard to watch them give you sad eyes, as if every moment of existence is torture.

/cue the Battle Hymn of the Republic

They are good. They have had millenia to hone their craft. We can salute them, but we cannot give in.