Based on the video: https://www.youtube.com/watch?v=u1cc1r_Y7M0

mouse.data <- data.frame(weight=c(0.9, 1.8, 2.4, 3.5, 3.9, 4.4, 5.1, 5.6, 6.3), size=c(1.4, 2.6, 1.0, 3.7, 5.5, 3.2, 3.0, 4.9, 6.3))
mouse.data

##   weight size
## 1    0.9  1.4
## 2    1.8  2.6
## 3    2.4  1.0
## 4    3.5  3.7
## 5    3.9  5.5
## 6    4.4  3.2
## 7    5.1  3.0
## 8    5.6  4.9
## 9    6.3  6.3

plot(mouse.data$weight, mouse.data$size)
mouse.regression <- lm(size ~ weight, data=mouse.data)
summary(mouse.regression)

## 
## Call:
## lm(formula = size ~ weight, data = mouse.data)
## 
## Residuals:
##     Min      1Q  Median      3Q     Max 
## -1.5482 -0.8037  0.1186  0.6186  1.8852 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)  
## (Intercept)   0.5813     0.9647   0.603   0.5658  
## weight        0.7778     0.2334   3.332   0.0126 *
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 1.19 on 7 degrees of freedom
## Multiple R-squared:  0.6133, Adjusted R-squared:  0.558 
## F-statistic:  11.1 on 1 and 7 DF,  p-value: 0.01256

abline(mouse.regression, col="blue")