T-Rex: Urushiol is the oil found on poison ivy! You won't see it or feel it, but it's absorbed within the skin within 10 minutes, and then you're doomed.

T-Rex: Doomed to have no ill effects, that is!

T-Rex: Touch poison ivy all you want, because it's not like you'll get itchy disgusting weeping blisters and possible nerve damage! Burn it and inhale the smoke, because it's not like you'll then get the same blisters caused by vapourized oils INSIDE YOUR FRIGGING LUNGS. Eat poison ivy leaves on your salad, because it's not like THAT will cause a particularly and possibly fatal bad time!

T-Rex: BECAUSE POISON IVY ONLY AFFECTS HUMANS.
Utahraptor: And for no real reason, right?

T-Rex: Yep! It certainly doesn't provide an advantage, because humans want to kill it. It's just a weird accident of evolution that humans can't even deal with its refreshing oils, and this is but one of the MANY reasons humans aren't as cool as they think they are. THEY CAN'T EVEN EAT POISON IVY.

Off panel: Or as we call it, "regular ivy".
T-Rex: Yes I was using their word and I apologize