Tear Jerker / Mars Needs Moms

• Milo and his mother's argument that kicks off the entire plot. His mom says that she wishes she didn't have to nag him so much, and Milo says that he wishes he didn't have a mother at all. She opens the door and simply looks at him in shock, indicating that he's gone a little over the edge. What really hammers it is her sad expression as she leaves. You can even see a tear go down her face if you look carefully.
• Gribble's backstory in general is one huge tearjerker. To start, he wasn't even a naughty boy. He was a good lad, listened to his mom, did everything he was told to do. As it turns out that's why the Martians wanted her. Like Milo, he followed the Martians in an attempt to rescue his mother. Unlike Milo, he failed to save his mother, as noted above. This left him alone on Mars. He's had no social contact with other humans for at least 25 years and has had to live with the burden of knowing that he is the reason his mom is gone. Is it any wonder he doesn't act like a normal human being? Chances are that he acts so comically in an attempt to mask the pain he feels.
  Milo: They took your mom, didn't they? It's OK, Grib. I know how you feel!
  Gribble: How I feel?! How I feel... you have no idea how I feel. (pulls out Martians' video camera) You see this? This is when they chose my mom. But way before they chose yours.
  Milo: I know, Gribble. It happened to me the same way.
  Gribble: (close to tears) No. No, you don't know. How could you possibly know? I was a good kid. I did my chores, put my things away. I did as I was told. Turns out that's exactly why they chose her... because of me. What kind of message is that to send to a little kid?
  Milo: I know. It's not fair!
  Gribble: I'll tell you what's not fair, man. Not fair is when a bunch of scary aliens take your mama - your only parent - away from you in the middle of the night. Not fair is when you follow them, and you sneak onto their ship, and you search but you can't find her. And then you see her... They got your mama strapped into some kind of machine. So I grabbed a couple of breathing helmets and I went to get her. But I didn't know what I know now. I didn't know that when the sun came up it'd start the machine. I didn't know what that machine was gonna do to her. Not until it was too late. And then I realized... I was all alone. I'd never see my mom again. And I'd never be able to tell her how much I loved her...
• When Milo's helmet shatters, and he starts suffocating due to lack of oxygen, his mother gives him her helmet so she can die instead, pulling a Heroic Sacrifice. Milo's crying and pleading for his mother not to die really brings this trope home. Luckily, Gribble managed to dig up the extra helmet that was meant for his mother.