[Jackal, being Jackal, understands the rarity of Yagyuu's smile, and therefore is pleased by the gesture in his usual straight-forward manner. while he may not know what he said to elicit that positive gesture, he does think that it's nice to see Yagyuu in good spirits.

what Yagyuu is saying is also fairly straightforward. he considers this, then nods, confident.]

Definitely sounds like somethin' worth lookin' into. [and because he invitation was implied in Yagyuu's speech, he figures that it doesn't hurt to say it outright.] I grew up with horses, so if you need an extra pair of hands for that experiment of yours, I wouldn't mind raisin' one.