Leo looked the most surprised that Marcus was resurrected.
Marcus was somewhat surprise when Leo said he is bionic.
Leo said he wanted to destroy Marcus, twice.
Marcus explains how he regenerates to Leo.
Marcus and Leo were going to finish each other off for the last time, but they were interrupted by Douglas.
Trivia[]
In the video game Detroit: Become Human there is also a rivalry/tension between an android named Markus and a human named Leo. Detroit was released after Lab Rats; it is unknown if this was meant as a reference or was named based on the Lab Rats pairing, but if not, it is an odd coincidence.