[shirike]

When Kruppe pulls Raest into his dream and Onos T'oolan strikes Raest to the floor, Kruppe mentions that Tool was called upon by the blood that filled his limbs before.

What does he mean?

[Aptorian]

Without the actual scene to read, I am going to assume Kruppe is simply referring to the ancient enmity between the two races. The Imass became Undead killing machines so that they could survive in the seemingly endless war against the much stronger Jaghut.

[Sinisdar Toste]

kruppes dream is a dream of a time before the ritual of tellann i'd say. tool was called to that time by the blood that he was at the time. the memory of it comes from k'rul, cuz he was around then, but kruppe makes it real.

[Gust Hubb]

Here's the quote for reference, and yes Apt you assumed correctly in thinking it was the T'lan ritual:

"He is Clanless, of course. Unbound and beyond binding, yet the ancient call commands him still--to his dismay. Imagine his surprise as being found out. Onos T'oolan, Sword of the First Empire, is once more called upon by the blood that once warmed his limbs, his heart, his life of so very long ago."

It could also be construed as the Imass' age old memory of suffering as mortals, but you will need to wait a couple more books for details on that story.