Nick had been very purposefully not holding on tight, as much as he might want to - still not used to one of his more recent pulses. Even after the push, his first instinct is to reach out to Lyall again, but he restrains himself. If whatever this is has got Lyall freaked out enough to push him away, he doubts trying to hold him again will help.

"What it is, what happened?"

Shit, please don't say he pulsed back toxic lips or skin or something.