I just had an odd thought... I don't know why, but I had a bit of an odd dream in which Tria was lying on her back... Later, I thought that her lying on her back could be used to tell Tops that she was pregnant with Tricia's egg. My idea was that when she realized that she was pregnant with the egg, she would be very happy, find Tops, tell him that she was happy and that something wonderful had happened, and when he asked what, she said she would show him. Tria would then proceed to lie down and stretch out on the sunny grass and ask Tops to look at her soft, white underbelly. When Tops said that she had a beautiful belly (not realizing the truth quite yet), she would ask him to look a bit lower... and he would see a bulge where the egg was.
Alternatively, if this were to be a slightly funny scene, Tops would be told to look at Tria's belly, and Tops, not knowing what Tria wanted him to find, would comment on her belly and how nice it looked and go on for some time, leading Tria to use one of her hind feet to grab one of his horns (using her toes) and direct his head down towards where the egg would be.
Something like this:
Tria: (Looks very happy) Topsy...
Tops: (Eating some leaves) Tria? (walks over to her)
Tria: (Standing on soft grass in the bright sun)... Hello, Topsy. Something wonderful has happened!
Tops: (Does not suspect that she is pregnant) Really? What is it?
Tria: Let me show you (laughs, then walks over to a part of the grass, lies down on her back, stretches out, and shows Tops her soft, white underbelly), come, look here.
Tops: Look at what, your belly? It's a very beautiful belly. It's so white, and soft and-
Tria: Look a bit lower.
Tops: Lower? (still sees her stomach) Oh yes, that part of your belly is just as beautiful as the upper part and-
Tria: (grabs one of his horns with her toes and pulls his head a bit lower)
Tops: Hey! What was that f- oh... your feet! You want me to look at your feet, and what wonderful feet they are, why, you have the best feet in the entire valley with three beautiful toes and you-
Tria: Look down.
Tops: Oh, your- (notices the bulge created by an egg) ... you have... an egg... in you
Tria (we can see her from above, lying on her stomach, we can see her white belly and the white soles of her feet, her toes having let go of Tops' horn) Uh, huh...
Tops: This is, this is...
Tria: We going to have a hatchling!
Tops: (No words, just a rare smile from this character.)