Counter mass Thor + SCVs as Zerg

Recently I've notice that Terrans do less bioball/tank against Zerg and go for a thor heavy play. The first problem with the mass thor push is that it's really difficult to distinguish from a standard mech play (hellions, tanks, thors) when you scout the Terran base (you just see "a lot" of factories with Techlabs on them).

The second problem is that this push often occurs before the Zerg player techs up to broodlords, which could be a pretty good counter to this.

What can Zerg do about it ?

As Artosis said, an army made mainly of Thors is quite immobile so you can abuse this with Mutalisks and Zerglings.

Neural Parasite from infestors are pretty good against thors and I've had lots of success running those against terran players. Fungal growth is great to have as well vs blink stalkers as well, so I really like infestors in general.