Don't test Tammy.
"What are we going to do today?" Tisa asks Tammy. "The weather is good outside today. Let's think about that walk."
In a confessional, Tisa explains that it's her goal to get Tammy out of that wheelchair, specifically to walk to the mailbox. "I want her to try," Tisa pleads. "But I think she's at a point where she's just scared and maybe a little embarrassed. But it's very important for her to do some kind of mobility."
Similarly, Tammy tells the camera that she doesn't think Tisa fully empathizes with her situation. "I don't think she quite understands what pain tolerance I have and what I go through, just to stand up and go the bathroom," Tammy explains. "I'm not scared of s––t."
Tisa tells Tammy, "If you think that you can't do it, I'm thinking that you can—and I know you can."
But Tammy just shuts her down: "I gave my answer. Don't push the issue," Tammy firmly says. "That's going to make me shut down more."
Watch the full clip above to see Tammy threaten to "cuss out" Tisa.
1000-lb Sisters airs Mondays at 10 p.m. on TLC.